Thin-gauge high-strength bridge steel plate and production method thereof

Abstract

The invention provides a thin-gauge high-strength bridge steel plate and a production method thereof, the steel plate comprises the following chemical components: C, Si, Mn, Cr, Cu, Ni, Nb, Ti, Al, a trace amount of S, P, H, and the balance of Fe and other inevitable impurities, and the production method is reduced to rolling after one-time heating. Through component optimization and process innovation, the bottlenecks of low efficiency, non-uniform performance, insufficient corrosion resistance and the like caused by twice rolling and dependence of a curling furnace in the prior art are broken through, and efficient production and comprehensive improvement of comprehensive performance of the thin bridge steel plate are realized.

Description

Technical Field

[0001] The invention relates to the technical field of steel processing, and in particular to a thin-gauge high-strength bridge steel plate and a production method thereof. Background Art

[0002] With the rapid development of long-span bridge construction, steel box girders have become the mainstream structural form of cross-sea bridges, suspension bridges and other bridges due to their advantages such as light weight, excellent seismic performance and convenient construction. U-shaped stiffening ribs (U ribs) in steel box girders require a large number of thin-gauge high-strength bridge steel plates with a thickness of 6-10mm, and the design specifications clearly require that such steel plates must be original rolled flat plates, and hot-rolled coils are prohibited. However, the existing wide and thick plate production lines have the following technical bottlenecks when manufacturing thin-gauge bridge steel: 1. The production process is complex and costly: The traditional process requires the continuous casting billet to be heated twice (averaging temperature ≥ 1200°C) and rolled twice (opening + finishing rolling), which results in a 30%-40% extension of the production cycle, an increase in energy consumption of more than 25%, a reduction in the yield rate, and a significant increase in production costs.

[0003] 2. The problem of plate shape control is prominent: thin-gauge steel plates (thickness ≤ 10mm) are prone to defects such as buckling, edge waves, and center waves during the rolling process. The unevenness is generally > 5mm / m, which seriously affects the subsequent welding and assembly accuracy.

[0004] 3. The contradiction between strength and toughness matching is intensified: In order to meet the design strength requirements of bridges (yield strength ≥ 420MPa), the existing process strengthens steel by increasing the carbon equivalent, but this causes the yield strength ratio to rise to above 0.92, the impact energy at -40℃ drops to below 60J, and the cold bending pass rate is less than 80%, which seriously threatens the structural safety.

[0005] 4. Insufficient corrosion resistance and service life: Traditional bridge steel has poor resistance to chloride ion corrosion in the marine atmospheric environment. The corrosion rate at the U-rib welds of cross-sea bridges can reach 0.3mm / year, and the service life is shortened by 30%-40% compared with the design requirements, resulting in a surge in subsequent maintenance costs.

[0006] In the prior art, patent CN114951267A proposes a method for directly rolling narrow and thin steel plates with 220mm billets in a single-frame furnace coil mill. Although it reduces one rolling process, it relies on repeated heating in the coiling furnace (coiling temperature ≥ 850℃), resulting in an increase of 1.2% in oxidation and burning rate, and it is impossible to produce steel plates with a width of > 3000mm. Although high-temperature rapid rolling reduces temperature drop, the final rolling temperature fluctuates greatly (750℃-850℃), which can easily lead to uneven organization, and it is difficult to coordinate the yield strength ratio and low-temperature toughness (-40℃ impact energy ≤ 60J). In addition, the coiling process equipment is complex, the maintenance cost is high, and the yield rate is only increased by 10%. Patent CN111889512B is a method for producing thin-gauge steel plates with a single-frame rolling mill. It uses a two-rolling process. Although the unevenness is controlled below 3mm / m, the billet after slitting needs to be heated twice, the grain coarsening problem is significant, and the elongation decreases by 5%-8%. It can be seen that the existing technology still finds it difficult to take into account the comprehensive requirements of efficient production of thin-gauge bridge steel, excellent plate shape, balance of strength and toughness, and long-term corrosion resistance. Summary of the invention

[0007] In order to solve the above-mentioned technical problems, the present invention provides a thin-gauge high-strength bridge steel plate and a production method thereof. Through composition optimization and process innovation, it breaks through the bottlenecks of low efficiency, uneven performance, insufficient corrosion resistance and other problems caused by double rolling and reliance on coiling furnaces in the prior art, thereby achieving efficient production of thin-gauge bridge steel plates and comprehensive improvement of their comprehensive performance.

[0008] To achieve the above object, the present invention proposes the following technical solutions: A thin gauge high strength bridge steel plate, the chemical composition of which, in terms of mass percentage, comprises: C: 0.055%-0.085%, Si: 0.20%-0.25%, Mn: 0.55%-0.65%, Cr: 0.88%-1.00%, Cu: 0.30%-0.40%, Ni: 0.10%-0.18%, Nb: 0.035%-0.045%, Ti: 0.010%-0.018%, Al: 0.03%-0.04%, S≤0.002%, P: 0.012%-0.019%, H≤0.00015%, the rest are Fe and other unavoidable impurities; Among them, Si, Cr, Cu, Ni, and P satisfy the following corrosion resistance index formula: [26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.10(%Ni)(%P)-33.39(%Cu) 2 ]≥6.5.

[0009] As a preferred technical solution of the present invention, the structural organization of the steel plate is a complex phase organization of ferrite + bainite, wherein the ferrite accounts for 25%-35% and the bainite accounts for 65%-75%.

[0010] The present invention also provides a method for producing a thin-gauge high-strength bridge steel plate, comprising the following steps: (1) Smelting and continuous casting: The molten iron is subjected to pre-desulfurization treatment, converter smelting to adjust the element composition, ladle refining, RH vacuum refining, and then continuously cast into billets, which are stacked and cooled; wherein the size of the billets is 220±10 mm in thickness, 1400±100 mm in width, and 2300-3800 mm in length; (2) Rolling: The billet is heated to 1230-1255° C., kept at this temperature for 220-280 min, and quickly sent to the feed end of the rolling mill, and directly rolled into a target steel plate with a thickness of 6-10 mm and a length of ≤40000 mm; The starting rolling temperature of the rolling mill is ≥1200°C, and the final rolling temperature is 830-870°C. During the rolling process, the reduction amount of the rolling mill rolls is dynamically controlled according to the temperature change. (3) Cooling after rolling: The target steel plate after rolling is cooled to 480-530℃ at a cooling rate of 15-25℃ / s, and then placed in a holding pit for insulation.

[0011] As a preferred technical solution of the present invention, the RH vacuum refining specifically comprises: degassing the ladle for at least 15 minutes at a vacuum degree of ≤2 mBar, and simultaneously performing soft stirring for at least 15 minutes.

[0012] As a preferred technical solution of the present invention, in step (2), before the billet is quickly delivered to the feed end of the rolling mill, roll scheduling is first performed, including: The billet is placed at the 40th to 80th block of the rolling mill's roll production sequence as the target billet to be rolled. Before rolling the target billet to be rolled, 6 to 10 blocks of the billet are first rolled into a steel plate transition material with a thickness specification of 8 to 14 mm, and the steel plate transition material is rolled from thick to thin.

[0013] As a preferred technical solution of the present invention, in the step (2), during the rolling process of the billet, the total rolling passes are ≤13 passes, wherein the billet is kept warm after the 6th pass, the start rolling temperature of the 7th pass is 1050-1060°C, and the last pass is a leveling pass.

[0014] As a preferred technical solution of the present invention, in step (2), during the rolling process of the billet, the rolling mill first bites into the billet at an initial speed of 2.0 m / s, linearly accelerates to 8.0 m / s after rolling for 1 m, and finally linearly decelerates for rolling and throws the steel after decelerating to 4.0 m / s.

[0015] As a preferred technical solution of the present invention, in step (2), during the rolling process of the billet, the cooling water of the rolling mill rolls is turned off before the billet is bitten, the cooling water of the rolling mill rolls is turned on after rolling for 1 m, and the cooling water of the rolling mill rolls is turned off when the remaining 2 m of rolling is completed.

[0016] As a preferred technical solution of the present invention, in the step (2), dynamically controlling the reduction amount of the rollers of the rolling mill according to the temperature change during the rolling process includes: When the rolling temperature is ≥1060℃, the reduction is dynamically controlled by the total torque of the double rolls of 5000-6000kN·m; When the rolling temperature is 960-1060℃, the reduction is regulated by the rolling force of 55000-66000kN and the bending roll force of 3000-4000kN; When the rolling temperature is less than 960℃, the rolling force and bending roll force are gradually reduced to reduce the amount of reduction.

[0017] As a preferred technical solution of the present invention, in step (2), during the billet rolling process, when the intermediate billet thickness is ≤32 mm, the roller cooling water is turned off, and the single-pass reduction meets the following conditions: When the intermediate blank thickness is 10-16mm, the single-pass pressing amount is greater than 3mm; When the intermediate blank thickness is less than 10mm, the single-pass pressing amount is greater than 1.5mm.

[0018] It can be seen from the above technical solutions that the technical solution of the present invention provides a thin-gauge high-strength bridge steel plate and a production method thereof, which has the following advantages over the traditional production method: (1) Without adding new equipment, the wide and thick plate production line can directly roll 220±10mm thick billets into 6-10mm thick bridge steel plates, reducing the original process of two heating and two rolling to one heating and one rolling, eliminating the intermediate billet opening process, shortening the production cycle, reducing energy consumption, improving the yield rate, and reducing production costs.

[0019] (2) Improve the welding performance of steel plates through low-carbon composition design, and improve the corrosion resistance of steel plates by adding elements such as Cr, Cu, Ni, and Si, thereby increasing the service life of steel plates and reducing maintenance costs.

[0020] (3) Improve the quality and straightness of the steel plate shape by scheduling the rolls and matching and controlling parameters such as billet heating temperature, reduction, rolling speed, rolling temperature, rolling thickness, rolling force, torque, and bending roll force.

[0021] (4) By controlling the upper and lower surface temperatures of the billet when it leaves the furnace, the cooling water of the rolling rollers, the cooling water of the roller table (the conveyor rollers used to transport the billet), rapid cooling after rolling, and insulation in the insulation pit, the temperature uniformity of the entire plate can be improved and the performance difference of the same plate can be reduced.

[0022] (5) During the RH vacuum refining process, the degassing time is guaranteed to be ≥15min and the soft stirring time is ≥15min, which can improve the purity of the steel plate and thus improve its comprehensive mechanical properties; the billet is stacked and cooled for a stacking cooling time of ≥48h, and the billet is placed in a heat preservation pit for heat preservation after rolling, which can enable the billet and steel plate to fully release hydrogen and improve the low-temperature toughness and cold forming performance of the steel plate.

[0023] (6) In the billet heating stage, the furnace temperature should be ≥1230℃. After the billet is taken out of the furnace, the transportation speed shall not be less than 6m / s, and the rolling temperature shall be ≥1200℃. This can effectively avoid the warping problem in the steel transfer stage and ensure that the plate quality meets the standard in the rolling process. At the same time, it helps to improve the rolling temperature of the steel plate. In addition, the total rolling pass is limited to ensure that the steel plate can reach the expected final rolling temperature. The heating temperature of the billet should be controlled at ≤1255℃ to avoid abnormal growth of the austenite structure. The billet holding time is controlled at 220-280min. When the billet is taken out of the furnace, the temperature difference between the upper and lower surfaces of the billet is controlled at ≤20℃, which can ensure that the billet reaches a fully "burned through" state. This can not only improve the uniformity of the billet temperature, but also promote the full solid solution of alloy elements. The uniform temperature of the billet is an important prerequisite for ensuring the uniform deformation of the steel plate, and improving the deformation uniformity is of great significance to improving the shape quality of the steel plate. In addition, the full solid solution of alloy elements is an important prerequisite for ensuring the strength of the steel plate.

[0024] (7) Low-speed biting and throwing can ensure the shape of the head and tail of the steel plate and prevent warping or buckling. High-speed rolling can prevent the final rolling temperature of thin gauges from being too low and ensure the final rolling temperature of the steel plate; secondly, it can improve production efficiency; thirdly, through the inertial traction of the steel plate's rapid movement, it can prevent the steel plate from running off and avoid the appearance of bevel angles, thus ensuring the shape of the steel plate.

[0025] (8) The control of roller cooling water is aimed at protecting the uniformity of the rolling temperature of the whole plate. The temperature drop at the head and tail is fast, and the temperature of the head and tail of the steel plate can be compensated by controlling the roller cooling water. If the final rolling temperature is too high, the microstructure grains are too coarse and the low-temperature toughness is poor; if the final rolling temperature is too low, the microstructure grains are too fine and the yield strength ratio is easy to exceed the standard; therefore, in order to ensure that the bridge steel plate has both good low-temperature toughness and a low yield strength ratio, the final rolling temperature must be strictly controlled. Therefore, the uniformity of the temperature of the whole plate is also a prerequisite for ensuring the uniformity of the performance of the steel plate.

[0026] (9) The rolling process adopts a torque-force-energy coordinated control strategy based on deformation resistance zoning: in the high temperature zone (≥1060℃), the low deformation resistance characteristics of the material are preferentially utilized, and the limit reduction is achieved by setting the upper limit of the total torque of the double rolls (5000-6000kNm); when the temperature drops to the medium and low temperature zone (960℃-1060℃), it switches to the rolling force-bending roll force coupling control mode (rolling force 55000-66000kN, bending roll force 3000-4000kN), and the roll gap convexity is actively increased by increasing the bending roll force to 3000-4000kN, forming an asymmetric reduction distribution of thinning in the middle and thickening at the edge, so as to suppress the deviation of the rolled piece and enhance the lateral stability; when the temperature is less than 960℃, a progressive load reduction procedure is implemented according to the work hardening effect, and the rolling force and bending roll force are progressively reduced. After rolling, a flattening pass is added to make the plate shape flatter, which is also a prerequisite for ensuring uniform cooling of the steel plate.

[0027] (10) The smaller the single-pass reduction, the more significant the temperature drop. For example, when the intermediate billet is 9 mm, the temperature drop is about 70°C when the single-pass reduction is 0.7 mm; the temperature drop is about 30°C when the single-pass reduction is 2 mm. The faster the temperature drop of the steel plate, the more difficult it is to ensure the final rolling temperature; and the lower the final rolling temperature, the more difficult it is to control the plate shape. Therefore, when producing thin-gauge steel plates, the single-pass reduction of the next few passes must be ensured to avoid too fast a temperature drop.

[0028] (11) When the intermediate billet thickness is ≤32mm, turning off the roller cooling water can reduce the heat loss of the rolled piece. When the intermediate billet thickness is ≤14mm, a low-temperature black band along the width direction is likely to appear when the intermediate billet stays on the roller. Therefore, turning off the roller cooling water can also ensure the temperature uniformity of the steel plate.

[0029] (12) The lower the rolling temperature, the greater the deformation resistance of the steel plate, and the more difficult it is to control the plate shape. If the rolling temperature is too low, the microstructure grains will be too fine, which is not good for the yield strength ratio of the steel plate. If the final rolling temperature is too high, it will be not good for the low-temperature toughness. Therefore, the final rolling temperature is controlled at 830-870℃.

[0030] (13) Rapid cooling after rolling can refine the phase transformation structure and improve the strength, plasticity and toughness of the steel plate. (14) Insulation in the insulation pit can make full use of the residual heat of the steel plate, so that the steel plate can undergo uniform self-tempering in the insulation pit, which can not only ensure the shape of the steel plate, but also fully eliminate the residual stress caused by rolling and cooling of the steel plate, and eliminate the hard phase structure, thereby improving the low-temperature toughness of the steel plate.

[0031] (15) Ferrite + bainite dual phase microstructure design: bainite provides higher strength for the steel plate, and the evenly distributed ferrite microstructure provides lower yield strength and higher elongation for the steel plate, making the steel plate have good seismic resistance and cold forming performance.

[0032] It should be appreciated that all combinations of the foregoing concepts, as well as additional concepts described in greater detail below, may be considered to be part of the inventive subject matter of the present disclosure, provided such concepts are not mutually inconsistent.

[0033] The foregoing and other aspects, embodiments and features of the present invention can be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as the features and / or beneficial effects of the exemplary embodiments, will be apparent from the following description or learned from the practice of the specific embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings are not drawn to scale according to actual reference objects. In the accompanying drawings, each identical or nearly identical component shown in various figures may be represented by the same reference numeral. For the sake of clarity, not every component is labeled in each figure. Now, embodiments of various aspects of the present invention will be described by way of example and with reference to the accompanying drawings, in which: Figure 1 This is a 500-fold magnified microstructure photograph of 1 / 2 of the longitudinal section of the bridge steel plate produced in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meanings understood by people with ordinary skills in the field to which the present invention belongs.

[0036] The words "first", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular form of "a", "an" or "the" and similar words do not indicate a quantity limitation, but indicate the existence of at least one. Words such as "include" or "comprise" mean that the elements or objects appearing before "include" or "comprise" include the features, wholes, steps, operations, elements and / or components listed after "include" or "comprise", and do not exclude the existence or addition of one or more other features, wholes, steps, operations, elements, components and / or their collections.

[0037] In order to solve the technical problem that the existing technology still has difficulty in taking into account the comprehensive requirements of efficient production, excellent plate shape, strength and toughness balance and long-term corrosion resistance of thin-gauge bridge steel, the embodiment of the present invention provides a thin-gauge high-strength bridge steel plate and a production method thereof. Through component optimization and process innovation, it breaks through the bottlenecks of low efficiency, uneven performance, insufficient corrosion resistance and other problems caused by double rolling and reliance on coiling furnaces in the existing technology, and realizes the efficient production of thin-gauge bridge steel plates and the overall improvement of their comprehensive performance.

[0038] A thin-gauge high-strength bridge steel plate provided in an embodiment of the present invention has a chemical composition, measured by mass percentage, comprising: C: 0.055%-0.085%, Si: 0.20%-0.25%, Mn: 0.55%-0.65%, Cr: 0.88%-1.00%, Cu: 0.30%-0.40%, Ni: 0.10%-0.18%, Nb: 0.035%-0.045%, Ti: 0.010%-0.018%, Al: 0.03%-0.04%, S≤0.002%, P: 0.012%-0.019%, H≤0.00015%, the rest are Fe and other unavoidable impurities; among them, Si, Cr, Cu, Ni, P meet the following corrosion resistance index formula: [26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.10(%Ni)(%P)-33.39(%Cu) 2 ]≥6.5. Wherein, (%Cu) represents the mass percentage of copper element, and the same applies to other elements.

[0039] The thickness of the steel plate produced in the embodiment of the present invention is 6-10 mm, and the mechanical properties of the steel plate are as follows: yield strength ≥500 MPa, tensile strength ≥660 MPa, yield ratio ≤0.78, elongation ≥25%, -60°C impact energy KV2 ≥250 J; the strength difference of the same plate is ≤30 MPa, and the yield strength ratio difference of the same plate is ≤0.04; and the internal stress distribution at different positions of the steel plate is uniform, and the maximum value of the residual internal stress is <15 MPa; the unevenness of the steel plate is ≤2 mm / m; in addition, in the marine atmospheric environment, the annual average corrosion rate of the steel plate is less than 0.15 mm / a; Figure 1 As shown, the structural organization of the steel plate is a complex phase organization of ferrite + bainite, in which ferrite accounts for 25%-35% and bainite accounts for 65%-75%.

[0040] The following is a detailed analysis and explanation of the functions of the components contained in the steel plate and the selection of their amounts in combination with the corrosion resistance index formula provided in the embodiment of the present invention.

[0041] C: The C element is a solid solution strengthening element that can effectively improve the strength of the steel plate and has little effect on the yield strength ratio. However, the carbon element has an adverse effect on the corrosion resistance, welding performance and low-temperature toughness of the steel plate. In addition, when the carbon content exceeds 0.085%, it will enter the peritectic zone, and surface cracks are likely to occur in the billet during the continuous casting process. Therefore, the embodiment of the present invention controls the carbon content to 0.055%-0.085%.

[0042] Si: Si is a solid solution strengthening element that can improve the strength of steel plates and enhance the corrosion resistance of steel plates in natural environments, especially local corrosion resistance. However, steel plates with high silicon content have poor iron oxide scale peeling performance, and iron oxide scale is easy to remain, which has an adverse effect on the surface quality of the steel plate. In addition, high silicon content will have an adverse effect on welding performance and easily cause cold brittleness. Therefore, the silicon content is constrained by the corrosion resistance index formula [1.49 (% Si)], and the silicon content is controlled at 0.20%-0.25%.

[0043] Mn: Mn is a solid solution strengthening element that can improve the strength and hardness of the steel plate. Manganese, as an austenite stabilizing element, can expand the austenite zone and inhibit the formation of ferrite. However, excessive manganese content has an adverse effect on the welding performance of the steel plate. Therefore, the manganese content is controlled at 0.55%-0.65%.

[0044] Cr: Cr is also a solid solution strengthening element and can effectively improve the strength of the steel plate. Chromium is a stabilizing element in the ferrite zone and can inhibit the pearlite phase transformation. By controlling the cooling, a ferrite + bainite complex structure can be obtained, which can improve the strength of the steel plate while ensuring a low yield ratio and good plasticity. In addition, in a corrosive environment, chromium can also form a stable passivation film on the surface of the steel plate to prevent further corrosion of the steel plate. However, an excessively high content of chromium is not conducive to the welding performance of the steel plate. Therefore, the content of chromium is constrained by the corrosion resistance index formula [1.20 (%Cr)], and the content of chromium is controlled at 0.88%-1.00%.

[0045] Cu: The addition of Cu element can not only effectively improve the strength and impact toughness of the steel plate, but also enhance the corrosion resistance of the steel plate. After the addition of copper element, in the corrosive environment of the marine atmosphere, the copper in the steel plate will be segregated and gradually enriched with the melting of iron, and an oxide intermediate film will be formed between the corrosion interface and the copper-enriched layer, which will be adsorbed on the surface of the steel to prevent the corrosive medium from corroding the interior of the steel plate, and finally achieve the effect of corrosion resistance. However, the price of copper is relatively high, and when its content is high, it is not conducive to hot deformation processing. Therefore, the content of copper element is limited by the corrosion resistance index formula [26.01 (%Cu), 7.29 (%Cu) (%Ni), 33.39 (%Cu) 2 ], and control the copper content at 0.30%-0.40%.

[0046] Ni: Ni is an austenite stabilizing element that can significantly expand the austenite phase region of steel and refine the grains, thereby improving the toughness and hardenability of the material. In terms of mechanical properties, Ni enhances the strength of steel through a solid solution strengthening mechanism, while improving low-temperature impact toughness and reducing the material's sensitivity to stress concentration and fatigue crack growth. In addition, the addition of Ni can optimize the corrosion resistance of steel. After enrichment at the rust layer interface, it forms a selective ion barrier, inhibits chloride ion penetration and promotes the formation of a protective rust layer (γ-FeOOH), which is especially suitable for harsh environments such as marine splash zones. When Ni is added simultaneously with Cu and Cr, the structure of the corrosion-resistant layer formed by the three elements becomes denser through a synergistic effect, thereby significantly enhancing and optimizing the corrosion resistance of the steel plate. However, since Ni is a strategically scarce resource, practical applications need to give priority to multi-element synergistic substitution solutions to reduce costs. Therefore, the Ni content is constrained by the corrosion resistance index formula [3.88 (%Ni), 7.29 (%Cu) (%Ni), 9.10 (%Ni) (%P)], and the Ni content is controlled within 0.10%-0.18%.

[0047] Nb, Ti: When the billet is heated at high temperature, Nb and Ti solid solution atoms tend to be concentrated at the austenite grain boundary, which has a dragging effect on the bow deformation and migration of the grain boundary. Therefore, the growth of austenite grains during the heating process of the billet can be inhibited. The Nb and Ti carbonitrides precipitated during the rolling stage also have the effect of inhibiting austenite recrystallization and inhibiting the growth of grains after recrystallization. Therefore, trace amounts of Nb and Ti have a good fine grain strengthening effect. Fine grain strengthening can improve the strength of the steel plate without affecting the plasticity and toughness of the steel. During the heat preservation process in the heat preservation pit, the compounds of Nb and Ti elements are fully precipitated, and the precipitation strengthening effect is the best, which can further improve the strength and low temperature toughness of the steel plate. A trace amount of Nb can play a significant role. The effect of continuing to add is not obvious, but it will increase the alloy cost. When the content is too high, it is easy to produce large-sized impurities and form a brittle phase. Therefore, the content of Nb element is controlled at 0.035%-0.045%. However, if the Ti content is too high, it is easy to form large-sized inclusions, which is not good for low-temperature impact toughness. Therefore, the Ti content is controlled within 0.010%-0.018%.

[0048] Al: Al can effectively reduce the oxygen content in steel during steelmaking and play a strong deoxidation role. Aluminum can also inhibit surface corrosion and internal oxidation of steel, extending the service life of steel. Aluminum can refine the original austenite grains of steel and increase the temperature of steel grain coarsening. However, when the content of solid solution metal aluminum in steel exceeds a certain value, the austenite grains tend to grow and coarsen. Therefore, the content of aluminum is controlled at 0.03%-0.04%.

[0049] P: P element also has corrosion resistance and can also improve the strength of steel plates. However, phosphorus element will increase the low-temperature brittleness of steel, easily cause serious segregation, and increase welding sensitivity, which is not conducive to the welding performance of steel. Therefore, the content of phosphorus element is constrained by the corrosion resistance index formula [17.28 (%P), 9.10 (%Ni) (%P)], and the content of phosphorus element is controlled at 0.012%-0.019%.

[0050] S: S is a harmful element in steel. Sulfur exists in steel in the form of FeS. FeS and Fe form a low melting point (985°C) compound. The heating temperature of the billet is generally above 1100°C, so when the billet is heated, the premature melting of the FeS compound causes the billet to crack during forging and rolling. S also has an adverse effect on the welding performance of the steel plate and reduces the corrosion resistance of the steel. Therefore, the content of S is controlled to ≤0.002%.

[0051] H: H is also a harmful element in steel. H dissolved in steel can cause defects such as hydrogen embrittlement and white spots. Like O and N, H has very low solubility in solid steel. It melts into the molten steel at high temperature and does not have time to escape during cooling, so it accumulates in the organization to form high-pressure fine pores, which sharply reduce the plasticity, toughness and fracture toughness of the steel. In severe cases, it can cause cracks and brittle fractures. Therefore, the content of H is controlled to ≤0.00015%.

[0052] The corrosion resistance index formula disclosed in the embodiment of the present invention reflects that the technical means of the present invention maximizes the corrosion resistance of steel through the synergistic effect of multiple elements, while limiting the negative impact of excessive elements to achieve performance balance. The formula requires ≥6.5, and the balance of the component ratio is achieved through mathematical optimization, and the elements such as Cu, Ni, Cr, Si, P, etc. that have both improved the corrosion resistance of the steel plate and have adverse effects are constrained. The embodiment of the present invention has formulated a performance quantification standard. The formula transforms the complex multi-element interaction into a quantifiable index, provides a clear goal for component design, and avoids the inefficiency of the traditional empirical trial and error method. The formula constrains the content range of each element to ensure that the corrosion resistance of different batches of steel plates is consistent and meets the requirements of engineering specifications. Through regression analysis of experimental data, the nonlinear relationship between elements is revealed, such as the synergistic / antagonistic effect of Cu and Ni elements [7.29 (%Cu) (%Ni)], and the ratio is optimized. The nonlinear terms in the formula include quadratic terms such as 33.39 (%Cu) 2 And cross terms such as 7.29 (%Cu) (%Ni) and 9.10 (%Ni) (%P), indicating that the interaction between elements is not a simple linear superposition, but a nonlinear complex cross-effect. The formula quantifies the synergistic and antagonistic effects of multiple elements through nonlinear terms, solves the limitations of the traditional single element limit method, and ensures the comprehensive optimization of corrosion resistance, strength, and plasticity. In addition, the coefficients of each element are significantly different (for example, the coefficient of Cu is 26.01, which is much higher than that of Ni, 3.88), reflecting the primary and secondary relationship of their contribution to corrosion resistance.

[0053] The embodiment of the present invention also provides a method for producing a thin-gauge high-strength bridge steel plate, comprising the following steps: (1) Smelting and continuous casting: The molten iron is subjected to pre-desulfurization treatment to remove sulfur in the molten iron (too much sulfur will cause cracking of the steel plate); then the molten iron is mixed with other alloy elements (such as Cr, Cu, Ni, etc.) for smelting in a converter to adjust the elemental composition of the molten iron; then the molten steel is further purified by ladle refining to remove impurities; further RH vacuum refining is performed, specifically, degassing for at least 15 minutes at a vacuum degree of ≤2mBar, and soft stirring is performed for at least 15 minutes at the same time to reduce bubbles in the steel, improve the purity, and thus improve the comprehensive mechanical properties of the steel plate; finally, the billet is continuously cast into a billet with a size of 220±10mm in thickness, 1400±100mm in width, and 2300-3800mm in length (the length is cut according to the size of the final steel plate), and stacked cooling is performed for a stacking cooling time of ≥48h to slowly release internal stress and avoid deformation.

[0054] (2) Rolling: During the entire rolling process, the size of the billet is the same. However, in order to ensure the rolling quality of the target steel plate, a scientific production sequence arrangement strategy needs to be formulated. Therefore, the embodiment of the present invention performs the following roll scheduling before rolling.

[0055] Roller scheduling: the billet is placed at the 40th to 80th position of the rolling mill roll production sequence as the target billet to be rolled, and the wear of the roll is moderate at this time to ensure the plate shape accuracy; before rolling the target billet to be rolled, 6-10 billets are first rolled into steel plate transition materials with a thickness specification of 8-14mm (that is, the steel plate transition materials with a thickness specification of 8-14mm are rolled from the 30th to 34th billets, and before that, non-target steel plates with low requirements for thickness and / or plate shape can be rolled), and when rolling the steel plate transition materials, the transition is rolled from thick to thin, and the thickness gradient buffer is used to gradually converge the gap between the rolls to the required accuracy range of the target steel plate, and the rolling mill is gradually adjusted to a stable state, and then the parameters of the rolling mill are adjusted to roll the target steel plate with the required thickness specification (i.e., a steel plate with a thickness of 6-10mm). The out-of-roundness of the rolls used in the rolling mill is ≤0.4mm.

[0056] Billet heating: heat the billet to 1230-1255°C and keep it warm for 220-280 minutes to ensure uniform temperature inside the billet, so that the temperature difference between the upper and lower surfaces of the billet when it is out of the furnace is ≤20°C to avoid uneven deformation during rolling; use high-pressure water to remove the iron oxide scale on the surface of the billet after it is out of the furnace (dephosphorization treatment) to prevent it from being pressed into the steel plate during rolling.

[0057] High temperature rolling: The dephosphorized billet is quickly delivered to the feed end of the rolling mill, with a transport speed of ≥6m / s. The billet is directly rolled into a target steel plate with a thickness of 6-10mm and a length of ≤40000mm without opening the billet. The starting rolling temperature of the rolling mill is ≥1200℃ (reducing deformation resistance through high temperature rolling), and the final rolling temperature is 830-870℃ (to ensure grain refinement and improve the strength and toughness of steel). During the rolling process, the reduction of the rolling mill rolls is dynamically controlled according to the temperature change.

[0058] During the rolling process of the billet, the total rolling passes are ≤ 13 passes, and the fewer the rolling passes, the smaller the temperature drop. After the 6th rolling pass, the temperature is kept at 1050-1060°C, and the last pass is a leveling pass to eliminate residual stress and improve the flatness of the plate.

[0059] For speed control of the rolling process: at the beginning of rolling, the rolling mill bites into the billet at an initial speed of 2.0 m / s. After rolling for 1 m, the linear acceleration (acceleration 2.0 m / s 2 ), after 3s, it is accelerated to 8.0m / s for constant speed rolling; when the remaining 14m is reached, it is switched to linear deceleration (deceleration 2.0m / s 2 ) for rolling, and the steel is thrown after being decelerated to 4.0m / s after 2s.

[0060] For the cooling water control of the rolling process: the cooling water of the rolling mill rolls is turned off before the billet is bitten, the cooling water of the rolling mill rolls is turned on after rolling for 1m, and the cooling water of the rolling mill rolls is turned off when the remaining 2m of rolling is completed. The amount of cooling water used during rolling is the original water volume × 3 times the finished steel thickness%, where the original water volume is the cooling water consumption of the traditional process.

[0061] When the rolling temperature is ≥1060℃, the reduction is dynamically controlled by the total torque of the double rolls of 5000-6000kN·m; When the rolling temperature is 960-1060℃, the reduction amount is coordinated and controlled by the rolling force of 55000-66000kN and the bending roll force of 3000-4000kN; when the rolling temperature is less than 960℃, the rolling force, bending roll force and reduction amount are gradually reduced.

[0062] At the same time, when the thickness of the intermediate billet is ≤32mm, the roller cooling water is turned off, and the single-pass pressing amount meets the following requirements: when the thickness of the intermediate billet is 10-16mm, the single-pass pressing amount is greater than 3mm; when the thickness of the intermediate billet is less than 10mm, the single-pass pressing amount is greater than 1.5mm.

[0063] (3) Cooling after rolling: After rolling, the steel plate is quickly put into water with a water temperature of ≥780°C. After entering the water, it is cooled to 480-530°C at a cooling rate of 15-25°C / s, and then quickly lowered from the cooling bed and put into the insulation pit with a pit temperature of ≥420°C and an insulation time of ≥45min.

[0064] The steel plate production method of the embodiment of the present invention produces a steel plate with a thickness specification of 6-10mm by appropriately designing the chemical composition and the heating, rolling and cooling processes. Among them, the yield strength of the steel plate is ≥500MPa, the tensile strength is ≥660MPa, the yield strength ratio is ≤0.78, the elongation is ≥25%, and the impact energy of the steel plate at -60℃ KV2 is ≥250J; the strength difference of the same plate is ≤30MPa, and the yield strength ratio difference of the same plate is ≤0.04; the internal stress distribution at different positions of the steel plate is uniform, and the maximum residual internal stress is <15MPa; the unevenness of the steel plate is ≤2mm / m; in the marine atmosphere environment, the annual average corrosion rate of the steel plate is less than 0.15mm / a.

[0065] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. A person with ordinary knowledge in the technical field to which the present invention belongs may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the definition of the claims.

Claims

1. A thin gauge high strength bridge steel plate, characterized in that: The chemical composition of the steel plate includes, by mass percentage: C: 0.055%-0.085%, Si: 0.20%-0.25%, Mn: 0.55%-0.65%, Cr: 0.88%-1.00%, Cu: 0.30%-0.40%, Ni: 0.10%-0.18%, Nb: 0.035%-0.045%, Ti: 0.010%-0.018%, Al: 0.03%-0.04%, S≤0.002%, P: 0.012%-0.019%, H≤0.00015%, the rest are Fe and other unavoidable impurities; Among them, Si, Cr, Cu, Ni, and P satisfy the following corrosion resistance index formula: [26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.10(%Ni)(%P)-33.39(%Cu) 2 ]≥6.5。 2. The thin gauge high strength bridge steel plate according to claim 1, characterized in that: The structural organization of the steel plate is a complex phase organization of ferrite + bainite, wherein the ferrite accounts for 25%-35% and the bainite accounts for 65%-75%.

3. A method for producing a thin gauge high strength bridge steel plate as claimed in claim 1, characterized in that: The steps include: (1) Smelting and continuous casting: The molten iron is subjected to pre-desulfurization treatment, converter smelting to adjust the element composition, ladle refining, RH vacuum refining, and then continuously cast into billets, which are stacked and cooled; wherein the size of the billets is 220±10 mm in thickness, 1400±100 mm in width, and 2300-3800 mm in length; (2) Rolling: The billet is heated to 1230-1255° C., kept at this temperature for 220-280 min, and quickly sent to the feed end of the rolling mill, and directly rolled into a target steel plate with a thickness of 6-10 mm and a length of ≤40000 mm; The starting rolling temperature of the rolling mill is ≥1200°C, and the final rolling temperature is 830-870°C. During the rolling process, the reduction amount of the rolling mill rolls is dynamically controlled according to the temperature change. (3) Cooling after rolling: The target steel plate after rolling is cooled to 480-530℃ at a cooling rate of 15-25℃ / s, and then placed in a holding pit for insulation.

4. The method for producing thin gauge high strength bridge steel plate according to claim 3, characterized in that: The RH vacuum refining specifically comprises: degassing the ladle for at least 15 minutes at a vacuum degree of ≤2 mBar, and simultaneously performing soft stirring for at least 15 minutes.

5. The method for producing thin gauge high strength bridge steel plate according to claim 3, characterized in that: In the step (2), before the billet is quickly delivered to the feed end of the rolling mill, roll scheduling is first performed, including: The billet is placed at the 40th to 80th block of the rolling mill's roll production sequence as the target billet to be rolled. Before rolling the target billet to be rolled, 6 to 10 blocks of the billet are first rolled into a steel plate transition material with a thickness specification of 8 to 14 mm, and the steel plate transition material is rolled from thick to thin.

6. The method for producing thin gauge high strength bridge steel plate according to claim 3, characterized in that: In the step (2), during the rolling process of the billet, the total number of rolling passes is ≤13, wherein the billet is kept warm after the sixth rolling pass, the seventh rolling pass starts at a temperature of 1050-1060°C, and the last rolling pass is a leveling pass.

7. The method for producing thin-gauge high-strength bridge steel plates according to claim 6, characterized in that: In the step (2), during the rolling process of the billet, the rolling mill first bites into the billet at an initial speed of 2.0 m / s, and then linearly accelerates to 8.0 m / s for constant speed rolling after rolling for 1 m, and finally linearly decelerates for rolling and decelerates to 4.0 m / s before throwing the steel.

8. The method for producing thin-gauge high-strength bridge steel plates according to claim 7, characterized in that: In the step (2), during the rolling process of the billet, the cooling water of the rolling mill rolls is turned off before the billet is bitten, the cooling water of the rolling mill rolls is turned on after rolling for 1 m, and the cooling water of the rolling mill rolls is turned off when the remaining 2 m of rolling is completed.

9. The method for producing thin gauge high strength bridge steel plate according to claim 8, characterized in that: In the step (2), dynamically controlling the reduction amount of the rollers of the rolling mill according to the temperature change during the rolling process includes: When the rolling temperature is ≥1060℃, the reduction is dynamically controlled by the total torque of the twin rolls of 5000-6000kN·m; When the rolling temperature is 960-1060℃, the reduction is regulated by the rolling force of 55000-66000kN and the bending roll force of 3000-4000kN; When the rolling temperature is less than 960℃, the rolling force and bending roll force are gradually reduced to reduce the amount of reduction.

10. The method for producing thin gauge high strength bridge steel plate according to claim 9, characterized in that: In the step (2), during the billet rolling process, when the intermediate billet thickness is ≤32 mm, the roller cooling water is turned off, and the single-pass reduction meets the following conditions: When the thickness of the intermediate blank is 10-16mm, the single-pass pressing amount is greater than 3mm; When the intermediate blank thickness is less than 10mm, the single-pass pressing amount is greater than 1.5mm.

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