Steel coil for photovoltaic support and method for manufacturing thereof

Abstract

The application relates to a steel coil for a photovoltaic support and a preparation method thereof, and the preparation method comprises the following steps: obtaining a continuous casting blank; rolling the continuous casting blank to obtain a hot-rolled steel strip; and coiling the steel strip into a steel coil; according to mass percentage, the continuous casting blank comprises the following components: C: 0.05%-0.07%, Si: 0.65%-0.75%, Mn: 0.61%-0.70%, P: 0.066%-0.075%, S: 0.0061%-0.0070%, Cu: 0.13%-0.18%, Cr: 2.5%-2.7%, Ti: 0.036%-0.045%, Alt: 0.21%-0.24%, and the rest is Fe and inevitable impurities. The steel coil prepared by the application can better meet the new requirements of the development of the photovoltaic support.

Description

Technical Field

[0001] This invention belongs to the field of hot-rolled steel strip manufacturing technology, specifically relating to a steel coil for photovoltaic brackets and its preparation method. Background Technology

[0002] Photovoltaic brackets are important supporting structural components of photovoltaic power plants. They are used in harsh and variable environments with strong corrosion. During their service, photovoltaic brackets need to withstand static loads, wind loads, snow loads and other external effects.

[0003] Currently, the main raw materials used for photovoltaic brackets are Q235 and Q355 hot-dip galvanized steel parts with yield strength levels of 235MPa and 355MPa, respectively. Their strength is low, which cannot meet the requirements for lightweight and easy installation. They also require subsequent maintenance, resulting in high costs throughout their entire life cycle. In addition, the hot-dip galvanizing process causes serious environmental pollution.

[0004] Weathering steel photovoltaic (PV) brackets develop a dense protective rust layer on their surface during service, significantly improving their corrosion resistance. This rust layer is also self-healing after damage, eliminating the need for subsequent acid washing, painting, and maintenance. Therefore, using weathering steel to manufacture PV brackets offers advantages such as energy saving and environmental friendliness. To adapt to the development trend of photovoltaic power plants, weathering steel for PV brackets should possess advantages such as high strength, lightweight, high corrosion resistance, long lifespan, easy forming, easy welding, and low cost. Existing weathering steel products cannot yet fully meet these requirements.

[0005] There are currently no reports on low-alloy corrosion-resistant steel for photovoltaic brackets with good formability and its manufacturing methods. Summary of the Invention

[0006] To address all or part of the aforementioned problems, the present invention aims to provide a steel coil for photovoltaic brackets and its preparation method. The preparation method of the present invention makes it easier to produce hot-rolled steel coils; the resulting steel coils have good formability, good weldability, high strength, and excellent corrosion resistance.

[0007] According to one aspect of the present invention, a method for preparing a high-formability steel coil for a photovoltaic support is provided, comprising:

[0008] Continuous casting billets are obtained through pretreatment;

[0009] The continuously cast billet is heated and held at a constant temperature.

[0010] The continuously cast billet is rough-rolled using a roughing mill to obtain a strip billet;

[0011] The strip is finished by a finishing mill to obtain hot-rolled steel strip; and

[0012] The hot-rolled steel strip is cooled and then coiled into a steel coil.

[0013] The continuously cast billet comprises the following components by mass percentage:

[0014] C: 0.05%-0.07%, Si: 0.65%-0.75%, Mn: 0.61%-0.70%, P: 0.066%-0.075%, S: 0.0061%-0.0070%, Cu: 0.13%-0.18%, Cr: 2.5%-2.7%, Ti: 0.036%-0.045%, Alt: 0.21%-0.24%, with the remainder being Fe and unavoidable impurities. Furthermore, the continuously cast billet must satisfy Mn / Si ≥ 0.80.

[0015] Furthermore, the process of obtaining the continuous casting billet through pretreatment specifically involves: desulfurizing the molten iron through pretreatment, smelting in a top-and-bottom combined blowing converter, refining with LF and RH, and continuous casting of slabs to obtain the continuous casting billet; the thickness of the continuous casting billet is 180-230mm.

[0016] Furthermore, the heating and heat preservation treatment of the continuous casting billet further includes: loading the continuous casting billet into a walking beam furnace; and heating and heat preservation treatment of the continuous casting billet in the walking beam furnace.

[0017] The continuous casting billet has a tapping temperature of 1200-1220℃ and a cumulative furnace dwell time of 180-210 minutes.

[0018] Furthermore, the step of using a roughing mill to rough-roll the continuously cast billet to obtain a strip billet specifically involves controlling the initial rolling temperature of the roughing mill to be 1150-1170℃ and the final rolling temperature of the roughing mill to be 1080-1110℃, and using a roughing mill to roll the continuously cast billet to obtain a strip billet.

[0019] The thickness of the strip obtained from rough rolling is 28-40 mm. The rough rolling process consists of 7 passes, with the following reduction rates for each pass: Pass 1: 15.3-16.2%, Pass 2: 16.1-17.3%, Pass 3: 17.0-20.0%, Pass 4: 20.8-23.3%, Pass 5: 21.6-25.9%, Pass 6: 25.8-33.2%, and Pass 7: 34.4-47.6%.

[0020] Furthermore, the step of using a finishing mill to finish-roll the strip billet to obtain hot-rolled steel strip specifically involves controlling the initial rolling temperature of the finishing mill to be 1020-1070℃ and the final rolling temperature of the finishing mill to be 870-910℃, and using a finishing mill to finish-roll the strip billet to obtain hot-rolled steel strip.

[0021] The thickness of the hot-rolled steel strip obtained by finishing rolling is 1.5-4.0 mm. The finishing rolling adopts a 7-stand finishing mill, and the reduction rate of each stand is as follows: 1st stand 44.1-56.6%, 2nd stand 38.1-47.4%, 3rd stand 31.8-37.8%, 4th stand 23.3-32.0%, 5th stand 20.1-27.6%, 6th stand 15.8-19.0%, and 7th stand 9.8-16.3%.

[0022] Furthermore, the step of cooling the hot-rolled steel strip and then coiling the cooled hot-rolled steel strip into a steel coil specifically involves:

[0023] The hot-rolled steel strip transported on the laminar flow cooling roller conveyor is cooled. The cooling method of the hot-rolled steel strip on the laminar flow cooling roller conveyor is post-cooling. During the cooling process, the flow rate ratio of the cooling water in the upper and lower manifolds is 8:10. The coiling temperature is controlled at 580-620℃. The cooled hot-rolled steel strip is coiled into a steel coil using a coiler.

[0024] The present invention also provides a high-formability steel coil for photovoltaic brackets, which is prepared by any of the preparation methods described above.

[0025] Furthermore, the sum of the grades of all coarse and fine non-metallic inclusions in the steel coil is ≤2 grades;

[0026] The steel coil has a yield strength ≥460MPa, tensile strength ≥600MPa, elongation after fracture ≥23%, and passes the 180°d=a cold bending test.

[0027] After the steel coil was periodically immersed in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate relative to Q355B ordinary steel was ≤28%.

[0028] When the straight seam welded steel pipe processed from the steel coil is completely flattened (in complete contact with the pipe wall), there are no cracks in the base material.

[0029] As can be seen from the above technical solution, the steel coil for photovoltaic support and its preparation method provided by the present invention have the following beneficial effects:

[0030] The steel coils prepared using the method of this invention can better meet the new requirements for the development of photovoltaic brackets, such as high strength, lightweight, high corrosion resistance, long life, easy manufacturing, easy forming, easy welding, low cost, high efficiency, no painting required, no maintenance required, energy saving, and environmental protection. Attached Figure Description

[0031] The accompanying drawings are included in and form part of this specification, and together with the description, serve to explain the principles of the invention.

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0033] Figure 1 This is a flowchart of the preparation method according to an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of the base material after flattening is shown in the diagram, which is used to conduct a complete flattening (complete contact with the pipe wall) test on a straight seam welded steel pipe sample obtained by using the steel coil in the embodiment of the present invention. Detailed Implementation

[0035] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.

[0036] When a range of values ​​is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0037] An embodiment of the present invention provides a method for preparing a steel coil for a photovoltaic support, such as... Figure 1 As shown, it includes:

[0038] Step S001: Obtain the continuous casting billet through pretreatment;

[0039] Step S002: Heating and holding the continuously cast billet;

[0040] Step S003: The continuously cast billet is rough rolled using a roughing mill to obtain a strip billet;

[0041] Step S004: The strip is finished rolled using a finishing mill to obtain hot-rolled steel strip; and

[0042] Step S005: Cool the hot-rolled steel strip and then coil the cooled hot-rolled steel strip into a steel coil;

[0043] The continuously cast billet in step S001, by mass percentage, comprises the following components:

[0044] C: 0.05%-0.07%, Si: 0.65%-0.75%, Mn: 0.61%-0.70%, P: 0.066%-0.075%, S: 0.0061%-0.0070%, Cu: 0.13%-0.18%, Cr: 2.5%-2.7%, Ti: 0.036%-0.045%, Alt: 0.21%-0.24%, with the remainder being Fe and unavoidable impurities.

[0045] The steel coils prepared using the method of this invention have a tensile strength of over 600 MPa and high formability.

[0046] The reasons for the limitations on the chemical elements in the embodiments of the present invention are as follows:

[0047] Practice has shown that increasing the carbon (C) content is an effective and economical way to improve the strength of steel. However, as the C content increases, the steel's plasticity, impact toughness, weldability, formability, and corrosion resistance decrease. To achieve a tensile strength of over 600 MPa and high formability in the steel strip of this invention, while also considering weldability, corrosion resistance, and economy, the C content is controlled within the range of 0.05%-0.07%.

[0048] Si is not a precious alloying element. Practical experience has shown that its solid solution strengthening coefficient in ferrite is higher than that of Mn. Si is very effective in improving strength and corrosion resistance. However, excessively high Si content reduces material toughness and is detrimental to weldability. To achieve a tensile strength of over 600 MPa in the steel strip of this invention, and considering processing performance, weldability, and corrosion resistance while also taking into account economic efficiency, the Si content in this invention is controlled within the range of 0.65%-0.75%.

[0049] Practice has shown that manganese (Mn) can form a substitutional solid solution in steel, resulting in solid solution strengthening and a linear increase in yield strength and tensile strength. Mn is an austenite-forming element, stabilizing austenite, lowering the austenite transformation temperature (Ar3), increasing the ferrite nucleation rate, and reducing grain growth rate, thus refining the grain size. However, increasing the Mn content increases the carbon equivalent of the steel, which is detrimental to weldability. To achieve a tensile strength of over 600 MPa in the steel strip of this invention, while comprehensively considering processing performance, weldability, and economic efficiency, the Mn content in this invention is controlled within the range of 0.61%-0.70%.

[0050] Practice has shown that phosphorus (P) has the second-highest solid solution strengthening effect in steel after carbon (C), effectively improving its resistance to atmospheric corrosion. Among many alloying elements that improve corrosion resistance, P offers the best cost-effectiveness. However, P easily forms and precipitates Fe3P in steel, increasing its brittleness and hindering its weldability. P diffuses slowly in γ-ferric and α-ferric iron, easily forming segregation, which negatively impacts the steel's formability. To achieve a tensile strength of over 600 MPa in the steel strip of this invention, and considering processing performance, weldability, and corrosion resistance while also maintaining economic efficiency, the P content in this invention is controlled within the range of 0.066%-0.075%.

[0051] Practice has shown that high sulfur (S) content can lead to "hot brittleness" defects in steel during hot working. Adding manganese (Mn) to the steel to form MnS plastic inclusions can mitigate the harmful effects of S. However, during rolling, MnS extending along the rolling direction easily causes the steel strip to form a banded structure. This banded structure reduces the transverse impact toughness and formability of the steel strip, while also causing anisotropy in mechanical properties. S is detrimental to the corrosion resistance of steel, as sulfides in the steel can become sources of rust; therefore, the S content should be minimized as much as possible. However, controlling the S content too low will increase manufacturing costs and reduce production efficiency. Considering the uniformity of mechanical properties, processing performance, and corrosion resistance of the high-formability steel strip in the embodiments of the present invention, while also taking into account economy and production efficiency, the S content in the embodiments of the present invention is controlled within the range of 0.0061%-0.0070%.

[0052] Practical experience has shown that Cu forms precipitates on the surface of steel, acting as a cathode to anoly passivate the steel surface and accumulating in the rust layer, altering its structure and preventing Cl- from penetrating the matrix, thus effectively improving the corrosion resistance of steel. However, Cu has a low melting point (1083℃) and tends to segregate at grain boundaries during the heating process of continuously cast billets. Excessive Cu content can lead to network crack defects during hot rolling. Cu is also a relatively expensive alloying element, and excessive Cu content can increase product costs. Considering the hot working performance, surface quality, and corrosion resistance of the high-formability steel strip in this embodiment of the invention, while also taking into account economic efficiency, the Cu content in this embodiment of the invention is controlled within the range of 0.13%-0.18%.

[0053] Practice has shown that Cr has a solid solution strengthening effect, which can improve the hardenability and strength of steel. It can form a dense and uniform rust layer containing fine α-FeOOH on the matrix surface, accelerate the development of electrochemical corrosion products to a thermodynamically stable state, block the further penetration of corrosive media into the matrix, and reduce the corrosion rate of steel. However, when the Cr content is too high, carbides will precipitate at the grain boundaries, reducing the ductility and toughness of the steel, worsening its formability and weldability, and increasing the cost of the alloy. In order to achieve a tensile strength of over 600 MPa for the steel strip in the embodiments of the present invention, and considering corrosion resistance, ductility and toughness, processing performance, weldability, and economic efficiency, the Cr content in the embodiments of the present invention is controlled within the range of 2.5%-2.7%.

[0054] Practice has shown that Ti and C form nanoscale TiC precipitates during hot rolling, which have fine-grain strengthening and precipitation strengthening effects, improving the strength and toughness of steel. TiN, formed by Ti and N, can inhibit austenite grain growth during the heating process of continuously cast billets, which is beneficial for improving the strength, toughness, and weldability of steel. If the Ti content is high, on the one hand, coarse TiN precipitates are easily formed, becoming stress concentration points and microcrack initiations, reducing the forming and fatigue performance of photovoltaic brackets; on the other hand, the recovery rate of Ti is unstable, resulting in large fluctuations in mechanical properties. Therefore, excessively high Ti content increases the processing difficulty of photovoltaic brackets and reduces processing efficiency. Considering the strength, weldability, processing performance, and service performance of the high-formability steel strip in this embodiment of the invention, the Ti content is controlled within the range of 0.036%-0.045%.

[0055] Practical experience has shown that in marine atmospheric environments, Al and Si have a synergistic effect, resulting in a rust layer that effectively blocks corrosive media and moisture. The fine AlN formed by Al and N can inhibit austenite grain growth during the heating process of continuously cast billets, refining the grain size and improving the strength, toughness, and weldability of the steel. However, excessively high Al content leads to the formation of more Al2O3 inclusions, which reduces the purity of the steel, its impact resistance, corrosion resistance, and surface quality. Furthermore, it easily clogs the nozzle during continuous casting, increasing production difficulty, reducing production efficiency, and raising alloy and manufacturing costs. Considering the strength, weldability, machinability, corrosion resistance, and surface quality of the high-formability steel strip in this embodiment of the invention, while also taking into account production difficulty, efficiency, and economy, the Alt content in this embodiment is controlled within the range of 0.21%-0.24%.

[0056] In step S001, the continuously cast billet also needs to satisfy Mn / Si≥0.80.

[0057] Practical experience has shown that if Mn / Si < 0.80, the oxygen content in the weld is high, leading to abnormal weld microstructure and a significant decrease in low-temperature impact toughness. Cracks of varying lengths can also sometimes be observed. Considering the weldability of the high-formability steel strip in this embodiment of the invention, the Mn / Si ratio is controlled to be ≥ 0.80.

[0058] The selection of C, Si, Mn, P, S, Cu, Cr, Ti, and Alt has a synergistic effect. By controlling the content of each element within the above range, the effects of solid solution strengthening, grain refinement strengthening, and phase transformation strengthening can be fully utilized, giving the high-formability low-alloy corrosion-resistant steel for photovoltaic brackets high purity, high strength, and excellent cold working performance.

[0059] The selection of the contents of Si, P, S, Cu, Cr and Alt has a synergistic effect. By controlling the contents of each element within the above range, a dense internal rust layer can be formed on the surface of the steel matrix, giving the high-formability low-alloy corrosion-resistant steel for photovoltaic brackets high corrosion resistance, meeting the service requirements of photovoltaic brackets, eliminating the need for subsequent pickling, painting and maintenance, and saving energy and protecting the environment.

[0060] The above-mentioned C, Mn, S, Cu, and Alt element contents, as well as the selection of Mn / Si, have a synergistic effect. By controlling the contents of each element and Mn / Si within the above ranges, defects such as hot-rolled network cracks can be avoided. This gives the high-formability low-alloy corrosion-resistant steel for photovoltaic brackets excellent hot working performance, high surface quality, and excellent welding performance, which can meet the stringent processing and service requirements of photovoltaic brackets.

[0061] The content of all the above elements and the selection of Mn / Si have a synergistic effect. By controlling the content of all elements and Mn / Si within the above range, the high-formability low-alloy corrosion-resistant steel for photovoltaic brackets is easy to process, has high production efficiency, low manufacturing cost, and short delivery cycle.

[0062] Specifically, step S001, obtaining the continuous casting billet through pretreatment, involves: desulfurizing the molten iron through pretreatment, smelting in a top-and-bottom combined blowing converter, refining with LF and RH, and continuous casting of slabs to obtain the continuous casting billet; the thickness of the continuous casting billet is 180-230mm.

[0063] Practice has shown that, given a fixed width and length of the continuously cast billet, a thicker billet results in higher output and yield, but also a greater mill load and greater fluctuations in the final rolling temperature, microstructure, and mechanical properties of the finished steel strip along its length. Furthermore, the billet thickness is limited by the maximum allowable outer diameter of the coil. Taking all these factors into account, this embodiment of the invention controls the continuously cast billet thickness to be 180-230 mm.

[0064] The step S002, which involves heating and holding the continuously cast billet, further includes: loading the continuously cast billet into a walking beam furnace; and heating and holding the continuously cast billet inside the walking beam furnace.

[0065] The furnace exit temperature of the continuously cast billet is 1200-1220℃, and the cumulative furnace dwell time of the continuously cast billet is 180-210 minutes.

[0066] Practice has shown that if the tapping temperature of the continuously cast billet is below 1200℃, the austenite grains can be refined, but the billet has poor thermoplasticity, high deformation resistance, and is difficult to hot-deform, thus leading to low subsequent rolling mill operating rates. If the tapping temperature is above 1220℃, although the billet's thermoplasticity increases, its deformation resistance decreases, and it is more prone to hot deformation, resulting in higher subsequent rolling mill operating rates, the austenite grains tend to coarsen. Considering the above factors, this embodiment of the invention controls the tapping temperature of the continuously cast billet to 1200-1220℃. If the cumulative furnace dwell time of the continuously cast billet is less than 180 minutes, its microstructure is not easily homogenized, rolling energy consumption is high, and equipment accidents are prone to occur. If the cumulative furnace dwell time of the continuously cast billet is longer than 210 minutes, it is prone to oxidation and decarburization, which increases energy consumption and reduces rolling mill operating rates and production efficiency. Considering the above factors, this embodiment of the invention controls the cumulative furnace dwell time of the continuously cast billet to 180-210 minutes.

[0067] Specifically, step S003 involves using a roughing mill to rough-roll the continuously cast billet to obtain a strip billet. This involves controlling the initial rolling temperature of the roughing mill to be 1150-1170℃ and the final rolling temperature of the roughing mill to be 1080-1110℃, and using a roughing mill to roll the continuously cast billet to obtain a strip billet.

[0068] Practice has shown that multiple recrystallizations during rough rolling can effectively refine austenite grains and obtain a uniform and fine austenite microstructure. If the initial rough rolling temperature is too high, austenite grain inhomogeneity will occur, leading to differences in strip microstructure and affecting the uniformity of the finished product's mechanical properties. If the initial rough rolling temperature is too low, the difficulty of strip shape control increases, the mill load and rolling energy consumption rise, which is detrimental to smooth rolling. Taking all these factors into consideration, the embodiments of this invention control the initial rough rolling temperature at 1150-1170℃ and the final rough rolling temperature at 1080-1110℃.

[0069] The thickness of the strip obtained from rough rolling is 28-40 mm. The rough rolling process consists of 7 passes, with the following reduction rates for each pass: 15.3-16.2% for the first pass, 16.1-17.3% for the second pass, 17.0-20.0% for the third pass, 20.8-23.3% for the fourth pass, 21.6-25.9% for the fifth pass, 25.8-33.2% for the sixth pass, and 34.4-47.6% for the seventh pass. See Table 1 for details.

[0070] Table 1. Rough rolling process (reduction rate of each pass) for a steel coil used in photovoltaic brackets.

[0071] Rolling passes First round Second lane 3rd lane 4th lane 5th course 6th lane 7th lane Pass reduction rate (%) 15.3-16.2 16.1-17.3 17.0-20.0 20.8-23.3 21.6-25.9 25.8-33.2 34.4-47.6

[0072] Practice has shown that if the strip is too thick and the reduction rate in the roughing passes is too small, partial recrystallization is likely to occur, leading to mixed crystal formation. This negatively impacts the uniformity of the mechanical properties of the finished steel strip and increases the rolling load and energy consumption of the finishing mill, affecting finishing stability. Conversely, if the strip is too thin and the reduction rate in the roughing passes is too large, it hinders the improvement of strip shape quality and increases the rolling load and energy consumption of the roughing mill, making rolling difficult and preventing the necessary finishing temperature for rolling the 1.5-4.0mm thin-gauge finished steel strip of this invention. It may even increase the rolling load and energy consumption of the finishing mill. Considering these factors, the embodiment of this invention controls the strip thickness to be 28-40mm. Based on the mechanical performance parameters of the roughing mill, the thickness of the continuously cast billet and the strip, a reasonable number of rolling passes for the roughing mill can be calculated to be 7. In this embodiment, the reduction rate in each roughing pass is controlled within the range shown in Table 1.

[0073] Specifically, step S004 involves using a finishing mill to finish-roll the strip to obtain hot-rolled steel strip. This involves controlling the initial rolling temperature of the finishing mill to be 1020-1070℃ and the final rolling temperature to be 870-910℃, and then using a finishing mill to finish-roll the strip to obtain hot-rolled steel strip.

[0074] Practice has shown that if the finishing rolling start temperature is too high, partial recrystallization can easily occur in the first stand (F1) and the second stand (F2), leading to mixed crystallization problems and abnormal fluctuations in the microstructure and mechanical properties of the finished steel strip. If the finishing rolling start temperature is too low, the desired final rolling temperature cannot be guaranteed. Taking all the above factors into consideration, the finishing rolling start temperature in this embodiment of the invention is controlled at 1020-1070℃.

[0075] Practice has shown that if the finishing rolling temperature is too high, the finished steel strip will have a coarsened microstructure and reduced strength and toughness; if the finishing rolling temperature is too low, the finished steel strip will have increased strength but decreased plasticity, resulting in an unreasonable strength-plasticity balance. This also reduces the rolling stability of the finishing mill, making it more difficult to control the thickness, width, and cross-sectional shape of the steel strip, and in severe cases, may lead to scrapped steel strip and equipment damage. Taking all these factors into consideration, this embodiment of the invention controls the finishing rolling temperature to 870-910℃.

[0076] The thickness of the hot-rolled steel strip obtained by finishing rolling is 1.5-4.0 mm. The finishing rolling adopts a 7-stand finishing mill. The reduction rate of each stand is as follows: 1st stand (F1) 44.1-56.6%, 2nd stand (F2) 38.1-47.4%, 3rd stand (F3) 31.8-37.8%, 4th stand (F4) 23.3-32.0%, 5th stand (F5) 20.1-27.6%, 6th stand (F6) 15.8-19.0%, and 7th stand (F7) 9.8-16.3%, as shown in Table 2.

[0077] Table 2. Finishing process of steel coils for photovoltaic brackets (reduction rate of each stand)

[0078] Rack number F1 F2 F3 F4 F5 F6 F7 Pass reduction rate (%) 44.1-56.6 38.1-47.4 31.8-37.8 23.3-32.0 20.1-27.6 15.8-19.0 9.8-16.3

[0079] The choice between using a 7-stand finishing mill depends on the actual equipment configuration, and the thickness of the finished steel strip is 1.5-4.0mm, which is the user's choice.

[0080] Practice has shown that if the reduction rate of each stand in the finishing mill is lower than the lower limit specified in Table 2, grain inhomogeneity will occur, and plasticity will decrease. If the reduction rate is higher than the upper limit specified in Table 2, the deformation resistance and load of each stand in the finishing mill will increase, leading to potential equipment hazards. Taking all the above factors into consideration, the reduction rates of each stand in the finishing mill are determined as shown in Table 2.

[0081] Specifically, step S005 involves cooling the hot-rolled steel strip and coiling it into a steel coil. This includes cooling the hot-rolled steel strip transported on the laminar flow cooling roller conveyor, wherein the cooling method on the laminar flow cooling roller conveyor is post-cooling, and the cooling water flow ratio between the upper and lower manifolds is 8:10 during the cooling process; and controlling the coiling temperature to be 580-620℃, and using a coiler to coil the cooled hot-rolled steel strip into a steel coil.

[0082] Practice has shown that, compared with other cooling methods, post-cooling is more conducive to the complete precipitation of ferrite, resulting in uniform ferrite grain size, reduced solid carbon content within the ferrite grains, and increased density of movable dislocations. This leads to a better match between the strength, plasticity, and cold forming properties of the finished steel strip.

[0083] Furthermore, the use of post-cooling allows the 1.5-4.0mm thin-gauge finished steel strip of this embodiment to run smoothly on the laminar flow cooling roller conveyor, ensuring successful coiling and avoiding rolling accidents such as coiling and steel piling. Taking all the above factors into consideration, the cooling method for the hot-rolled steel strip on the laminar flow cooling roller conveyor in this embodiment is post-cooling.

[0084] Practice has shown that if the cooling water flow ratio between the upper and lower manifolds is higher or lower than 8:10, it will cause a significant difference in the cooling rate between the upper and lower surfaces of the steel strip, leading to fluctuations in microstructure and mechanical properties, and increasing the difficulty of shape control. Taking all the above factors into consideration, the embodiment of the present invention controls the cooling water flow ratio between the upper and lower manifolds to be 8:10.

[0085] Practice has shown that by properly controlling the coiling temperature, the γ→α phase transformation temperature can be appropriately reduced, increasing the α phase nucleation rate and refining the ferrite grains. Simultaneously, a moderate increase in the proportion of bainite in the microstructure, with bainite grains being finer than ferrite (approximately 1 μm) and possessing a higher dislocation density, can improve the overall mechanical properties of the steel strip. Furthermore, properly controlling the coiling temperature is also a necessary measure to reduce the difficulty of controlling the strip shape and coil shape. Taking all the above factors into consideration, the coiling temperature in this embodiment of the invention is controlled at 580-620℃.

[0086] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of these embodiments. Experimental methods not specifically described in the following embodiments are performed according to conventional methods and conditions.

[0087] Examples 1-3:

[0088] The preparation methods of Examples 1-3 of this invention include the following steps:

[0089] First, continuously cast billets are obtained through hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF and RH refining, and slab continuous casting. The chemical composition of the continuously cast billets obtained in Examples 1 to 3 is shown in Table 3.

[0090] Table 3 Chemical composition (mass percentage) of continuously cast billets in Examples 1-3 of this invention

[0091] C Si Mn P S Cr Cu Ti Alt Mn / Si ratio Example 1 0.062 0.72 0.69 0.071 0.0066 2.62 0.16 0.044 0.23 0.95 Example 2 0.066 0.66 0.68 0.067 0.0063 2.58 0.15 0.042 0.22 1.03 Example 3 0.055 0.69 0.63 0.073 0.0068 2.67 0.17 0.037 0.21 0.91

[0092] Secondly, the continuously cast billet is heated, rough rolled, finish rolled, and cooled to obtain hot-rolled steel strip, which is then coiled to obtain hot-rolled steel coil. The process parameters for each process are shown in Tables 4 and 5, and the properties of the obtained steel coil are shown in Table 6.

[0093] Table 4. Heating and roughing process parameters for Examples 1-3 of the present invention.

[0094]

[0095] Table 5. Finishing rolling, cooling, and coiling process parameters for Examples 1-3 of the present invention.

[0096]

[0097]

[0098] Table 6 Performance of the steel coils obtained in Examples 1-3 of the present invention

[0099]

[0100] As can be seen from Tables 3-6, the steel coils prepared in Examples 1-3 of this invention differ significantly from ordinary weathering steel in chemical composition, heating, rough rolling, finish rolling, cooling, and other process parameters. Significant differences also exist in microstructure and various properties. The high-formability, low-alloy corrosion-resistant steel for photovoltaic brackets provided by this invention can better meet the new requirements for photovoltaic bracket development, such as high strength, lightweight, high corrosion resistance, long lifespan, ease of manufacturing, ease of forming, ease of welding, low cost, high efficiency, no painting required, maintenance-free, energy saving, and environmental protection.

[0101] The preparation method of this invention optimizes the content of elements such as C, Si, Mn, P, S, Cu, Cr, Ti, and Alt, and controls the Mn / Si ratio, continuous casting billet exit temperature, furnace dwell time, roughing rolling start and finish rolling temperatures, rolling passes, strip thickness, pass reduction rate, finishing rolling start and finish rolling temperatures, rolling passes, finished product thickness, reduction rate of each stand, cooling method, cooling water flow ratio of upper and lower manifolds, and coiling temperature, so that the sum of the grades of various coarse and fine non-metallic inclusions in the obtained finished steel is ≤2 grades; and the obtained steel coil has a yield strength ≥460MPa, tensile strength ≥600MPa, elongation after fracture ≥23%, passes the 180°d=a cold bending test, and after cyclic immersion in a 0.01mol / L NaHSO3 solution for 72 hours, the corrosion rate relative to Q355B ordinary steel is ≤28%. Figure 2 As shown, when the straight seam welded steel pipe sample processed from the steel coil of this embodiment is completely flattened (in complete contact with the pipe wall), there are no cracks in the base material.

[0102] The steel coils prepared by the method of this invention have low levels of harmful and impurity elements, resulting in pure steel. They exhibit high strength, reducing weight by 22% compared to Q235B galvanized steel sheets, demonstrating significant weight reduction. They possess strong corrosion resistance, meeting the service requirements of photovoltaic brackets. Excellent formability satisfies the stringent processing requirements of photovoltaic brackets. Moderate P and Al content, and low Cu and Ti content, avoid their adverse effects on plasticity, toughness, weldability, and surface quality, resulting in stable mechanical properties, low manufacturing difficulty, and high production efficiency. Free from precious alloying elements such as Ni, Nb, V, and Mo, and with low Mn content, the alloy cost is lower. No subsequent pickling, coating, or maintenance is required, making it energy-saving, environmentally friendly, with short delivery cycles and low operating costs.

[0103] The steel coils prepared by the preparation method of this invention can better meet the new requirements for the development of photovoltaic brackets, such as high strength, lightweight, high corrosion resistance, long life, easy manufacturing, easy forming, easy welding, low cost, high efficiency, no painting required, no maintenance, energy saving, and environmental protection.

[0104] This invention also provides a steel coil for photovoltaic brackets, which is prepared by the preparation method of any of the above embodiments.

[0105] Among them, the sum of the grades of various coarse and fine non-metallic inclusions in the steel coil is ≤2.

[0106] The steel coil has a yield strength ≥460MPa, tensile strength ≥600MPa, elongation after fracture ≥23%, and passes the 180°d=a cold bending test.

[0107] After the steel coil was periodically immersed in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate was ≤28% compared to ordinary Q355B steel.

[0108] When the straight seam welded steel pipe sample made from steel coil is completely flattened, there are no cracks in the base material.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for manufacturing a steel coil for a photovoltaic support, characterized in that, include: Continuous casting billets are obtained through pretreatment; The continuously cast billet is heated and held at a constant temperature. The continuously cast billet is rough-rolled using a roughing mill to obtain a strip billet; The strip billet is finished by a finishing mill to obtain hot-rolled steel strip; as well as The hot-rolled steel strip is cooled and then coiled into a steel coil. The continuously cast billet, by mass percentage, consists of the following components: C: 0.05%-0.07%, Si: 0.65%-0.75%, Mn: 0.61%-0.70%, P: 0.066%-0.075%, S: 0.0061%-0.0070%, Cu: 0.13%-0.18%, Cr: 2.5%-2.7%, Ti: 0.036%-0.045%, Alt: 0.21%-0.24%, with the remainder being Fe and unavoidable impurities. Furthermore, the continuously cast billet must satisfy Mn / Si ≥ 0.

80.

2. The preparation method according to claim 1, characterized in that, The process of obtaining a continuously cast billet through pretreatment specifically involves: desulfurization of molten iron through pretreatment, smelting in a top-and-bottom combined blowing converter, refining with LF and RH, and continuous casting of slabs to obtain a continuously cast billet; the thickness of the continuously cast billet is 180-230mm.

3. The preparation method according to claim 1, characterized in that, The heating and heat preservation treatment of the continuous casting billet further includes: loading the continuous casting billet into a walking beam furnace; and heating and heat preservation treatment of the continuous casting billet in the walking beam furnace; The continuous casting billet has a tapping temperature of 1200-1220℃ and a cumulative furnace dwell time of 180-210 minutes.

4. The preparation method according to claim 1, characterized in that, The process of using a roughing mill to rough-roll the continuously cast billet to obtain a strip billet specifically involves controlling the initial rolling temperature of the roughing mill to be 1150-1170℃ and the final rolling temperature of the roughing mill to be 1080-1110℃, and using a roughing mill to roll the continuously cast billet to obtain a strip billet.

5. The preparation method according to claim 4, characterized in that, The thickness of the strip obtained from rough rolling is 28-40 mm. The rough rolling process consists of 7 passes, with the following reduction rates for each pass: Pass 1: 15.3-16.2%, Pass 2: 16.1-17.3%, Pass 3: 17.0-20.0%, Pass 4: 20.8-23.3%, Pass 5: 21.6-25.9%, Pass 6: 25.8-33.2%, and Pass 7: 34.4-47.6%.

6. The preparation method according to claim 1, characterized in that, The process of using a finishing mill to finish rolling the strip to obtain hot-rolled steel strip specifically involves controlling the initial rolling temperature of the finishing mill to be 1020-1070℃ and the final rolling temperature of the finishing mill to be 870-910℃, and then using a finishing mill to finish rolling the strip to obtain hot-rolled steel strip.

7. The preparation method according to claim 6, characterized in that, The thickness of the hot-rolled steel strip obtained by finishing rolling is 1.5-4.0 mm. The finishing rolling adopts a 7-stand finishing mill, and the reduction rate of each stand is as follows: 1st stand 44.1-56.6%, 2nd stand 38.1-47.4%, 3rd stand 31.8-37.8%, 4th stand 23.3-32.0%, 5th stand 20.1-27.6%, 6th stand 15.8-19.0%, and 7th stand 9.8-16.3%.

8. The preparation method according to claim 1, characterized in that, The process of cooling the hot-rolled steel strip and then coiling the cooled hot-rolled steel strip into a steel coil specifically involves: The hot-rolled steel strip being transported on the laminar flow cooling roller conveyor is cooled. The cooling method for the hot-rolled steel strip on the laminar flow cooling roller conveyor is post-cooling. The cooling water flow ratio of the upper and lower manifolds is 8:

10. The coiling temperature is controlled at 580-620℃. The cooled hot-rolled steel strip is then coiled into a steel coil using a coiler.

9. A steel coil for a photovoltaic support structure, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The steel coil according to claim 9, characterized in that, The sum of the grades of all coarse and fine non-metallic inclusions in the steel coil is ≤2 grades; The steel coil has a yield strength ≥460MPa, tensile strength ≥600MPa, elongation after fracture ≥23%, and passes the 180°d=a cold bending test. After the steel coil was periodically immersed in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate relative to Q355B ordinary steel was ≤28%. When the straight seam welded steel pipe processed from the steel coil is completely flattened, the base material has no cracks.

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