High corrosion resistant low alloy steel for photovoltaic support and method for manufacturing the same

Abstract

The application discloses a kind of high corrosion-resistant low alloy steel for photovoltaic support and manufacturing method thereof, solve the technical problems such as high manufacturing cost, poor comprehensive performance, low production efficiency.The composition of the high corrosion-resistant low alloy steel includes C:0.11%-0.13%, Si:0.65%-0.79%, Mn:0.31%-0.50%, P:0.020%-0.030%, S:0.0041%-0.0049%, Cr:3.7%-3.9%, Cu:0.13%-0.18%, Alt:0.08%-0.12%, Sn≤0.015%, As≤0.025%, Sb≤0.015%, the rest is Fe and inevitable impurities, high corrosion-resistant low alloy steel satisfies Sn+As+Sb≤0.050%, (Sn+As+Sb) / Cu≤0.28.The manufacturing method of high corrosion-resistant low alloy steel includes smelting, continuous casting, continuous casting blank heating, heat preservation, rough rolling, finish rolling, cooling, coiling.The application can reduce manufacturing cost, improve steel performance and improve production efficiency.

Description

Technical Field

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

[0002] In recent years, guided by the goal of clean energy transformation, the development of renewable energy has been unstoppable. Solar energy has significant advantages such as being clean, safe, inexhaustible, and readily available. Photovoltaic power generation is the fastest-growing power generation technology, and its increase in power generation accounts for a steadily increasing proportion of the global increase in total power generation.

[0003] Photovoltaic support systems are specialized equipment installed in photovoltaic power plants to support, fix, and rotate photovoltaic modules. They represent the most material-intensive link in the photovoltaic industry chain. With the trend towards high-power development, photovoltaic power plants are experiencing increased module weight and support system load. They are often built in harsh and variable environments such as deserts, Gobi, wastelands, and saline-alkali lands, placing extremely high demands on the self-weight, load-bearing capacity, corrosion resistance, and stability of photovoltaic support systems.

[0004] Currently, photovoltaic (PV) brackets are mainly made of plain carbon steel as the base material, and hot-dip galvanizing or zinc-aluminum-magnesium galvanizing is used to improve the corrosion resistance of PV brackets. However, the production process of PV brackets has problems such as environmental pollution, increased production steps, extended process flow, and increased manufacturing costs. Furthermore, during transportation, processing, and installation, the coating on the surface of PV brackets is easily damaged, causing corrosion of the base material. Post-maintenance is necessary to prevent premature failure.

[0005] Moreover, most of the weathering steel used in existing photovoltaic brackets contains high levels of precious metal elements, which increases production costs. In addition, the overall performance of the steel is relatively poor, and there are also problems such as high production difficulty and low production efficiency, which need to be improved. Summary of the Invention

[0006] In order to solve all or part of the above problems, the present invention aims to provide a high corrosion-resistant low alloy steel for photovoltaic brackets and a method for manufacturing the same, which can reduce manufacturing costs, achieve lightweighting, and improve the overall performance of the steel, while also reducing production difficulty and improving production efficiency.

[0007] In a first aspect, the present invention provides a high corrosion-resistant low-alloy steel for photovoltaic brackets, wherein the composition of the high corrosion-resistant low-alloy steel comprises, by mass percentage: C: 0.11%-0.13%, Si: 0.65%-0.79%, Mn: 0.31%-0.50%, P: 0.020%-0.030%, S: 0.0041%-0.0049%, Cr: 3.7%-3.9%, Cu: 0.13%-0.18%, Alt: 0.08%-0.12%, Sn≤0.015%, As≤0.025%, Sb≤0.015%, with the remainder being Fe and unavoidable impurities;

[0008] The high corrosion-resistant low alloy steel satisfies Sn+As+Sb≤0.050% and (Sn+As+Sb) / Cu≤0.28.

[0009] Optionally, the high corrosion-resistant low-alloy steel has the following properties:

[0010] Yield strength ≥620MPa, tensile strength ≥750MPa, elongation after fracture ≥19%, and pass the 180°d=a cold bending test;

[0011] After 72 hours of cyclic immersion in a mixed solution of NaHSO3 and 3.5% NaCl with an initial concentration of 0.01 mol / L, the corrosion rate was ≤30% relative to Q355B ordinary steel and ≤50% relative to Q450NQR1 general weathering steel.

[0012] Secondly, the present invention provides a method for manufacturing high corrosion-resistant low-alloy steel, comprising the following steps:

[0013] S1, through hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining and slab continuous casting, to obtain a continuously cast billet with a thickness of 180-230mm;

[0014] S2, the continuously cast billet is loaded into a walking beam furnace for heating and heat preservation;

[0015] S3 uses a roughing mill to roll the continuously cast billet to obtain a strip billet;

[0016] S4 uses a finishing mill to roll the strip billet to obtain hot-rolled steel strip;

[0017] S5, hot-rolled steel strip is cooled during transport on a laminar flow cooling roller conveyor;

[0018] S6, hot-rolled steel strip is wound into hot-rolled steel coils by a coiler.

[0019] Optionally, in S2, the continuous casting billet tapping temperature is controlled at 1180℃-1200℃ and the cumulative furnace dwell time is 180-210 minutes.

[0020] Optionally, in S3, the continuously cast billet is rough rolled in 7 passes, and the rough rolling start temperature is controlled at 1130℃-1150℃, the rough rolling finish temperature is controlled at 1060℃-1100℃, and the strip thickness is controlled at 28-40mm.

[0021] Optionally, in S3, the absolute reduction for each roughing pass is as follows: 35.1-37.3mm, 32.1-34.3mm, 28.4-32.7mm, 28-30.9mm, 23.6-26.7mm, 21.7-25.3mm, and 21-24.2mm.

[0022] Optionally, in S4, the strip is finished rolled by a 7-stand finishing mill, and the finishing rolling start temperature is controlled at 1000℃-1050℃, the finishing rolling finish temperature is controlled at 850℃-890℃, and the hot-rolled steel strip thickness is controlled at 1.5-4.0mm.

[0023] Optionally, in S4, the absolute reduction of each stand in the finishing mill is as follows: 14.31-18.64mm, 5.57-8.95mm, 2.44-4.47mm, 1.28-2.46mm, 0.80-1.5mm, 0.36-0.9mm, and 0.17-0.64mm.

[0024] Optionally, in S5, the hot-rolled steel strip is cooled in the laminar flow cooling roller table by the rear section cooling method, and the ratio of cooling water flow rate of the upper and lower manifolds is controlled to be 2:3.

[0025] Optionally, in S6, the hot-rolled steel strip winding temperature is controlled at 570℃-610℃ during the hot-rolled steel strip winding process.

[0026] As can be seen from the above technical solution, the high corrosion-resistant low alloy steel for photovoltaic brackets and its manufacturing method provided by the present invention have the following advantages:

[0027] This high-corrosion-resistant low-alloy steel has low levels of harmful and impurity elements, resulting in high purity and strength. Replacing Q235B galvanized steel can reduce weight by 30%, demonstrating significant lightweighting effects. Its strong corrosion resistance meets the requirements of photovoltaic mounting systems. Furthermore, its excellent formability satisfies the stringent processing requirements of photovoltaic mounting systems.

[0028] Meanwhile, the high corrosion-resistant low alloy steel has moderate P and Al content and low Cu and Ti content, which avoids its adverse effects on plasticity, toughness, weldability, surface quality, etc., making the mechanical properties of the high corrosion-resistant low alloy steel more stable and easier to manufacture, thereby improving production efficiency.

[0029] Furthermore, this high corrosion-resistant low-alloy steel contains no precious alloying elements such as Ni, Nb, V, and Mo, and has a low Mn content, effectively reducing alloy costs. At the same time, photovoltaic brackets made from this high corrosion-resistant low-alloy steel require no subsequent pickling, painting, or maintenance, offering advantages such as energy saving, environmental friendliness, short delivery cycles, and low operating costs.

[0030] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0031] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the technical solutions of the present invention, and do not constitute a limitation on the technical solutions of the present invention.

[0032] Figure 1 This is a flowchart illustrating the manufacturing method of high corrosion-resistant low alloy steel in an embodiment of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be arbitrarily combined with each other.

[0034] like Figure 1 The illustration shows an embodiment of the present invention, which discloses a high corrosion-resistant low-alloy steel for photovoltaic brackets. The composition of the high corrosion-resistant low-alloy steel, by mass percentage, includes: C: 0.11%-0.13%, Si: 0.65%-0.79%, Mn: 0.31%-0.50%, P: 0.020%-0.030%, S: 0.0041%-0.0049%, Cr: 3.7%-3.9%, Cu: 0.13%-0.18%, Alt: 0.08%-0.12%, Sn≤0.015%, As≤0.025%, Sb≤0.015%, with the remainder being Fe and unavoidable impurities. Simultaneously, the high corrosion-resistant low-alloy steel satisfies Sn+As+Sb≤0.050% and (Sn+As+Sb) / Cu≤0.28.

[0035] The reasons for the restrictions on each chemical element in this embodiment are as follows:

[0036] 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 750 MPa for the steel strip in this embodiment, and considering corrosion resistance, processing performance, and weldability while also maintaining economic efficiency, this invention controls the C content within the range of 0.11%-0.13%.

[0037] Practice has shown that Si is not a precious alloying element. 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 the toughness of the material and is not conducive to improving weldability. To achieve a tensile strength of over 750 MPa for the steel strip of this invention, and considering corrosion resistance, processing performance, and weldability, while also taking into account economic efficiency, the Si content of this invention is controlled within the range of 0.65%-0.79%.

[0038] Practical experience has shown that manganese (Mn) is an austenite-forming element that stabilizes austenite, lowers the austenite transformation temperature, increases the ferrite nucleation rate, and reduces grain growth rate, thus refining the grain size. Mn can form substitutional solid solutions in steel, resulting in solid solution strengthening and a linear increase in yield strength and tensile strength. However, increasing the Mn content increases the carbon equivalent in the steel, which is detrimental to weldability. To achieve a tensile strength of over 750 MPa in the steel strip of this invention, while comprehensively considering processing performance, weldability, and economic efficiency, the Mn content is controlled within the range of 0.31%-0.50%.

[0039] 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 leading to segregation, which negatively impacts the steel's formability. To achieve a tensile strength of over 750 MPa in the steel strip of this invention, and considering processing performance, weldability, and corrosion resistance while also maintaining economic efficiency, the P content is controlled within the range of 0.020%-0.030%.

[0040] Practical experience has shown that sulfur (S) is detrimental to the corrosion resistance of steel, and sulfides in steel can become sources of rust. High S content can lead to "hot brittleness" defects in steel. 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, reducing the transverse impact toughness and formability of the steel strip, while also leading to anisotropy in mechanical properties. Therefore, the S content should be reduced as much as possible. However, controlling the S content too low will increase manufacturing costs and reduce production efficiency. Considering the corrosion resistance, uniformity of mechanical properties, and processing performance of the high corrosion-resistant steel strip of this invention, while also taking into account economy and production efficiency, this invention controls the S content within the range of 0.0041%-0.0049%.

[0041] Practical experience has shown that Cu is an effective element for improving the corrosion resistance of steel. It forms precipitates on the steel surface and acts as a cathode to cause anodic passivation of the steel surface. It also accumulates in the rust layer, altering the structure of the rust layer and inhibiting the growth of Cl. - Cu penetrates the matrix. 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 increases product costs. Considering the corrosion resistance, hot working performance, and surface quality of the high corrosion-resistant steel strip of this invention, while also taking into account economic efficiency, this invention controls the Cu content within the range of 0.13%-0.18%.

[0042] Practical experience has shown that Cr can form a dense and uniform rust layer containing fine α-FeOOH on the substrate surface, accelerating the development of electrochemical corrosion products towards a thermodynamically stable state, preventing further penetration of corrosive media into the substrate, and reducing the corrosion rate of steel. Cr has a solid solution strengthening effect, which can improve the hardenability and strength 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. To achieve a tensile strength of over 750 MPa for the steel strip of this invention, and considering corrosion resistance, ductility and toughness, processing performance, weldability, and economic efficiency, the Cr content of this invention is controlled within the range of 3.7%-3.9%.

[0043] Practice has shown that the fine AlN formed by Al and N can inhibit austenite grain growth during the heating process of continuously cast billets, thus refining the grains and improving the strength, toughness, and weldability of steel. Al has great potential in improving the corrosion resistance and reducing the cost of steel. Under marine atmospheric conditions, Al-Si alloyed steel has a synergistic effect in improving the corrosion resistance of steel, and the generated FeAl2O4 fine-grained spinel oxide can enhance the barrier effect of the rust layer against corrosive media and moisture. However, excessively high Al content will lead to the formation of more Al2O3 inclusions, which on the one hand reduces the purity of the steel and the impact resistance, corrosion resistance, and surface quality of the steel strip; on the other hand, it is very easy to clog the nozzle during continuous casting, increasing production difficulty, reducing production efficiency, and increasing alloy and manufacturing costs. Taking into account the strength, weldability, machinability, impact resistance, corrosion resistance, and surface quality of the high corrosion-resistant steel strip of this invention, and balancing production difficulty, production efficiency, and economy, this invention controls the Al content in the range of 0.08%-0.12%.

[0044] Practical experience has shown that residual elements such as Sn, As, and Sb have low melting points. During the high-temperature cooling and reheating process of continuously cast billets, they precipitate between the matrix and iron scale, forming liquid enriched phases. These phases then penetrate to the grain boundaries and extend into surface network cracks during subsequent rolling. To avoid this type of defect, the content of individual Sn, As, and Sb, as well as their total amount, should be limited. As the ratio of (Sn+As+Sb) / Cu increases, the melting point of Cu decreases, and the sensitivity to hot-rolled network crack defects caused by Cu segregation at grain boundaries increases. Considering the corrosion resistance, processing performance, and surface quality of the high-tensile-strength corrosion-resistant steel strip of this invention, the following parameters are controlled: Sn ≤ 0.015%, As ≤ 0.025%, Sb ≤ 0.015%, Sn+As+Sb ≤ 0.050%, and (Sn+As+Sb) / Cu ≤ 0.28.

[0045] In this embodiment, the content of the elements C, Si, Mn, P, S, Cu, Cr, Alt, Sn, As, and Sb, as well as the selection of Sn+As+Sb, have a synergistic effect. By controlling the content of each element and Sn+As+Sb within the above range, the effects of solid solution strengthening, grain refinement strengthening, and phase transformation strengthening can be fully utilized, so that the high corrosion-resistant low alloy steel for photovoltaic brackets has high purity, high strength, and excellent cold working performance.

[0046] Secondly, the selection of the contents of the aforementioned elements 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 corrosion-resistant low alloy steel high corrosion resistance, which can meet the service requirements of photovoltaic brackets, eliminating the need for subsequent pickling, painting, and maintenance, and saving energy and protecting the environment.

[0047] Meanwhile, the selection of the contents of C, Mn, S, Cu, Alt, Sn, As, and Sb elements, as well as Sn+As+Sb and (Sn+As+Sb) / Cu, has a synergistic effect. By controlling the contents of each element and Sn+As+Sb and (Sn+As+Sb) / Cu within the above ranges, defects such as hot-rolled network cracks can be avoided, giving the high corrosion-resistant low-alloy steel for photovoltaic brackets excellent hot working performance and high surface quality, which can meet the stringent processing and service requirements of photovoltaic brackets.

[0048] Moreover, the content of all the above elements and the selection of Sn+As+Sb and (Sn+As+Sb) / Cu have a synergistic effect. By controlling the content of all elements and Sn+As+Sb and (Sn+As+Sb) / Cu within the above range, the high corrosion-resistant low alloy steel for photovoltaic brackets is easy to process, has high production efficiency, low manufacturing cost, and short delivery cycle.

[0049] The high corrosion-resistant low-alloy steel in this embodiment has at least the following properties:

[0050] (1) The yield strength of high corrosion-resistant low alloy steel is ≥620MPa, the tensile strength is ≥750MPa, the elongation after fracture is ≥19%, and the cold bending test at 180°d=a is qualified.

[0051] (2) After being periodically immersed in a mixed solution of NaHSO3 and 3.5% NaCl with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate of high corrosion-resistant low alloy steel is ≤30% relative to Q355B ordinary steel and ≤50% relative to Q450NQR1 general weathering steel.

[0052] like Figure 1 As shown, this embodiment also discloses a method for manufacturing high corrosion-resistant low-alloy steel for photovoltaic brackets, including the following steps:

[0053] S1 is obtained by pre-treatment of hot metal for desulfurization, top and bottom combined blowing converter smelting, LF refining and slab continuous casting.

[0054] S2, the continuously cast billet is loaded into a walking beam furnace for heating and heat preservation;

[0055] S3 uses a roughing mill to roll the continuously cast billet to obtain a strip billet;

[0056] S4 uses a finishing mill to roll the strip billet to obtain hot-rolled steel strip;

[0057] S5, hot-rolled steel strip is cooled during transport on a laminar flow cooling roller conveyor;

[0058] S6, hot-rolled steel strip is wound into hot-rolled steel coil by a coiler;

[0059] In S1, the composition of the continuously cast billet is controlled by the following mass percentages: C: 0.11%-0.13%, Si: 0.65%-0.79%, Mn: 0.31%-0.50%, P: 0.020%-0.030%, S: 0.0041%-0.0049%, Cu: 0.13%-0.18%, Cr: 3.7%-3.9%, Alt: 0.08%-0.12%, Sn≤0.015%, As≤0.025%, Sb≤0.015%, with the remainder being Fe and unavoidable impurities. Furthermore, Sn+As+Sb in the continuously cast billet ≤0.050% and (Sn+As+Sb) / Cu≤0.28.

[0060] In S1, the thickness of the continuously cast billet is controlled at 180-230 mm. Practical experience has shown that, given a fixed billet width and length, a thicker billet results in higher output and yield, but also a higher 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 coiler. Therefore, considering all these factors, this embodiment controls the billet thickness at 180-230 mm.

[0061] In S2, the continuous casting billet exit temperature is controlled at 1180℃-1200℃, and the cumulative furnace dwell time is 180-210 minutes. Practice has shown that if the billet exit temperature is below 1180℃, the austenite grains can be refined, but the billet has poor thermoplasticity, high deformation resistance, and is difficult to hot-deform, resulting in low mill operating rate. If the billet exit temperature is above 1200℃, the austenite grains are more easily coarsened, but the billet's thermoplasticity increases, deformation resistance decreases, it is prone to hot deformation, and the mill operating rate is high. If the cumulative furnace dwell time is less than 180 minutes, the microstructure is not easily homogenized, rolling energy consumption is high, and equipment accidents are prone to occur. If the cumulative furnace dwell time is longer than 210 minutes, oxidation loss, decarburization, and energy consumption increase, while mill operating rate and production efficiency decrease. Therefore, taking all the above factors into account, the present invention controls the holding temperature and tapping temperature of the continuously cast billet to be 1180℃-1200℃.

[0062] In S3, the continuously cast billet is rough rolled in 7 passes, and the rough rolling start temperature is controlled at 1130℃-1150℃, the rough rolling finish temperature is controlled at 1060℃-1100℃, and the strip thickness is controlled at 28-40mm. The absolute reduction of the rough rolling is shown in Table 1.

[0063] Table 1 Absolute Reduction in Rough Rolling

[0064]

[0065] Practice has shown that the main metallurgical purpose of rough rolling is to disrupt the as-cast structure of the continuously cast billet, effectively refine the austenite grains through multiple recrystallizations, and obtain a uniform and fine austenite structure. If the rough rolling start temperature is too high, austenite grain inhomogeneity will occur, leading to differences in the strip structure and affecting the uniformity of the finished product's mechanical properties. If the rough rolling start temperature is too low, the difficulty of controlling the strip shape increases, the mill load and rolling energy consumption rise, which is not conducive to smooth rolling. Therefore, considering the above effects, this invention controls the rough rolling start temperature to 1130℃-1150℃ and the rough rolling finish temperature to 1060℃-1100℃.

[0066] Practice has shown that if the strip is too thick, the cumulative reduction rate and the reduction rate per pass in roughing will decrease, making it easier for partial recrystallization to occur, causing mixed crystal phenomena, which will have an adverse effect on the uniformity of the mechanical properties of the finished steel strip. At the same time, it will increase the rolling load and rolling energy consumption of the finishing mill, affecting the stability of finishing.

[0067] If the strip is too thin, it will be detrimental to improving the strip shape quality, increase the rolling load and energy consumption of the roughing mill, hinder smooth rolling, and make it impossible to guarantee the finishing mill's starting temperature required 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. Therefore, considering all these factors, this invention controls the strip thickness to be 28-40mm. Based on the roughing mill's energy parameters, the thickness of the continuously cast billet and the strip, the optimal number of rolling passes for the roughing mill can be calculated to be 7 passes.

[0068] Practice has shown that if the absolute reduction of the roughing mill is lower than the lower limit specified in Table 1, grain inhomogeneity will occur, reducing plasticity. If the absolute reduction is higher than the upper limit specified in Table 1, it will not only increase the deformation resistance and load of the roughing mill, but also cause the mill head to curl up, and in severe cases, "roll wrapping" accidents may occur, leading to equipment hazards. Taking all the above factors into consideration, the absolute reduction of the seven passes in the roughing mill is determined to be 35.1-37.3mm, 32.1-34.3mm, 28.4-32.7mm, 28-30.9mm, 23.6-26.7mm, 21.7-25.3mm, and 21-24.2mm respectively.

[0069] In S4, the strip is finished rolled by a 7-stand finishing mill, and the finishing rolling start temperature is controlled at 1000℃-1050℃, the finishing rolling finish temperature is controlled at 850℃-890℃, and the hot-rolled steel strip thickness is controlled at 1.5-4.0mm. The absolute reduction in finishing rolling is shown in Table 2.

[0070] Table 2 Absolute Reduction in Finishing Rolling

[0071]

[0072] Practice has shown that if the finishing rolling start temperature is too high, partial recrystallization can easily occur in the F1 and F2 finishing mill stands, leading to mixed crystal problems, differences in the microstructure of the finished steel strip, and abnormal fluctuations in mechanical properties. If the finishing rolling start temperature is too low, the desired final rolling temperature cannot be guaranteed. Therefore, taking all the above factors into consideration, this invention controls the finishing rolling start temperature to be 1000℃-1050℃.

[0073] 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. In severe cases, it can lead to scrapped steel strip and equipment damage. Taking all these factors into consideration, this invention controls the finishing rolling temperature to 850℃-890℃.

[0074] Practice has shown that 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.

[0075] Practice has shown that if the absolute reduction of each stand in the finishing mill is lower than the lower limit specified in Table 2, grain inhomogeneity will occur, reducing plasticity. If the absolute reduction 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 factors into consideration, the absolute reduction of each stand in the finishing mill is determined to be 14.31-18.64 mm, 5.75-8.95 mm, 2.44-4.47 mm, 1.28-2.46 mm, 0.80-1.50 mm, 0.36-0.90 mm, and 0.17-0.64 mm, respectively.

[0076] In S5, the hot-rolled steel strip is cooled in the laminar flow cooling roller table by the rear section cooling method, and the flow ratio of the cooling water in the upper and lower manifolds is controlled at 2:3.

[0077] 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 intragranular carbon content, and increased density of movable dislocations. This leads to a better balance of strength, toughness, plasticity, and cold forming properties in the finished steel strip. Furthermore, post-cooling ensures smooth operation of the hot-rolled steel strip on the laminar flow cooling roller conveyor, facilitating coiling and preventing rolling accidents such as coiling and piling. Therefore, considering all these factors, this invention employs post-cooling for the hot-rolled steel strip on the laminar flow cooling roller conveyor.

[0078] Practice has shown that if the cooling water flow ratio of the upper and lower manifolds is higher or lower than 2:3, it will cause a large difference in the cooling rate of the upper and lower surfaces of the steel strip, resulting in fluctuations in the microstructure and mechanical properties, and will also increase the difficulty of plate shape control. Therefore, taking into account the above factors, the present invention controls the cooling water flow ratio of the upper and lower manifolds to be 2:3.

[0079] In S6, the hot-rolled steel strip coiling temperature is controlled at 570℃-610℃ during the hot-rolled steel strip coiling process.

[0080] Practice has shown that by reasonably controlling the coiling temperature, the γ→α phase transformation temperature can be appropriately reduced, increasing the α phase nucleation rate, refining ferrite grains, and simultaneously increasing the proportion of bainite in the microstructure. Bainite grains are finer than ferrite grains, approximately 1 μm in size, and have a higher dislocation density, thus improving the overall mechanical properties of the steel strip. Furthermore, reasonably controlling the coiling temperature is also a necessary measure to reduce the difficulty of sheet and coil shape control. Taking all these factors into consideration, the coiling temperature in this invention is controlled at 570℃-610℃.

[0081] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods not specified in the following examples can be performed according to conventional methods and conditions.

[0082] Examples 1-3:

[0083] The chemical composition, process parameters, and performance of Examples 1-3 are shown in Tables 3-6.

[0084] Table 3 Chemical composition (mass percentage) of embodiments of the present invention

[0085]

[0086] Table 4 Heating and roughing process parameters of embodiments of the present invention

[0087]

[0088] Table 5 Finishing and cooling process parameters of the embodiments of the present invention

[0089]

[0090] Table 6 Performance of the embodiments of the present invention

[0091]

[0092]

[0093] As shown in Tables 3-6, the embodiments of the present invention differ significantly from those of general weathering steel in terms of chemical composition, heating, rough rolling, finish rolling, cooling and other process parameters, and their various properties also differ significantly. The high corrosion-resistant low alloy steel in the present invention can better meet the new requirements for the development of photovoltaic brackets, such as high strength, lightweight, high corrosion resistance, long service life, easy manufacturing, low cost, high efficiency, no painting required, no maintenance required, energy saving and environmental protection.

[0094] As can be seen from the above process, the high corrosion-resistant low alloy steel and its manufacturing method in this invention, through optimized design of the content of elements such as C, Si, Mn, P, S, Cu, Cr, Alt, Sn, As, and Sb, and by controlling Sn+As+Sb, (Sn+As+Sb) / Cu, continuous casting billet exit temperature and furnace dwell time, roughing rolling start and finish rolling temperature, rolling passes, strip thickness, absolute reduction, finishing rolling start and finish rolling temperature, rolling passes, finished product thickness, absolute reduction, cooling method, cooling water flow ratio of upper and lower manifolds, and coiling temperature, result in a finished steel yield strength ≥620MPa, tensile strength ≥750MPa, elongation after fracture ≥19%, and passing the 180°d=a cold bending test. Meanwhile, after being periodically immersed in a mixed solution of NaHSO3 and 3.5% NaCl with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate of high corrosion-resistant low alloy steel is ≤30% relative to Q355B ordinary steel and ≤50% relative to Q450NQR1 general weathering steel.

[0095] The high corrosion-resistant low-alloy steel of this invention has low content of harmful and impurity elements, is pure in quality, and has high strength. Replacing Q235B galvanized steel sheet can reduce weight by 30%, resulting in significant weight reduction. This high corrosion-resistant low-alloy steel exhibits strong corrosion resistance, meeting the service requirements of photovoltaic brackets. Furthermore, it possesses excellent formability, satisfying the stringent processing requirements of photovoltaic brackets.

[0096] Meanwhile, the high corrosion-resistant low alloy steel has moderate P and Al content and low Cu and Ti content, which avoids its adverse effects on plasticity, toughness, weldability, surface quality, etc., making the mechanical properties of the high corrosion-resistant low alloy steel more stable and easier to manufacture, thereby improving production efficiency.

[0097] Furthermore, this high corrosion-resistant low-alloy steel contains no precious alloying elements such as Ni, Nb, V, and Mo, and has a low Mn content, effectively reducing alloy production costs. Simultaneously, photovoltaic brackets made from this high corrosion-resistant low-alloy steel require no subsequent acid pickling, painting, or maintenance, offering advantages such as energy saving, environmental friendliness, short delivery cycles, and low operating costs.

[0098] It should be noted that, unless otherwise stated, the technical or scientific terms used in this invention should have the ordinary meaning as understood by one of ordinary skill in the art.

[0099] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0100] 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. 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, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. 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 high corrosion-resistant low-alloy steel for photovoltaic brackets, characterized in that, The composition of the high corrosion-resistant low alloy steel, by mass percentage, includes: C: 0.11%-0.13%, Si: 0.65%-0.79%, Mn: 0.31%-0.50%, P: 0.020%-0.030%, S: 0.0041%-0.0049%, Cr: 3.7%-3.9%, Cu: 0.13%-0.18%, Alt: 0.08%-0.12%, Sn≤0.015%, As≤0.025%, Sb≤0.015%, with the remainder being Fe and unavoidable impurities; The high corrosion-resistant low alloy steel satisfies Sn+As+Sb≤0.050% and (Sn+As+Sb) / Cu≤0.28; The high corrosion-resistant low alloy steel has the following properties: Yield strength ≥620MPa, tensile strength ≥750MPa, elongation after fracture ≥19%, and pass the 180°d=a cold bending test; After 72 hours of cyclic immersion in a mixed solution of NaHSO3 and 3.5% NaCl with an initial concentration of 0.01 mol / L, the corrosion rate was ≤30% relative to Q355B ordinary steel and ≤50% relative to Q450NQR1 general weathering steel. The manufacturing method of high corrosion-resistant low alloy steel includes the following steps: S1, through hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining and slab continuous casting, to obtain a continuously cast billet with a thickness of 180-230mm; S2, the continuously cast billet is loaded into a walking beam furnace for heating and heat preservation; S3 uses a roughing mill to roll the continuously cast billet to obtain a strip billet; S4 uses a finishing mill to roll the strip billet to obtain hot-rolled steel strip; S5, hot-rolled steel strip is cooled during transport on a laminar flow cooling roller conveyor; S6, hot-rolled steel strip is wound into hot-rolled steel coil by a coiler; In S3, the continuously cast billet is rough rolled in 7 passes, and the rough rolling start temperature is controlled at 1130℃-1150℃, the rough rolling finish temperature is controlled at 1060℃-1100℃, and the billet thickness is controlled at 28-40mm. In S4, the strip is finished rolled using a 7-stand finishing mill, with the initial finishing temperature controlled at 1000℃-1050℃, the final finishing temperature at 850℃-890℃, and the hot-rolled strip thickness at 1.5-4.0mm. In S5, the hot-rolled steel strip is cooled in the laminar flow cooling roller table by the rear section cooling method, and the flow ratio of the cooling water in the upper and lower manifolds is controlled at 2:

3.

2. The method for manufacturing high corrosion-resistant low-alloy steel according to claim 1, characterized in that, In S2, the continuous casting billet tapping temperature is controlled at 1180℃-1200℃, and the cumulative furnace dwell time is 180-210 minutes.

3. The method for manufacturing high corrosion-resistant low-alloy steel according to claim 1, characterized in that, In S4, the absolute reduction of each stand in the finishing mill is as follows: 14.31-18.64mm, 5.57-8.95mm, 2.44-4.47mm, 1.28-2.46mm, 0.80-1.5mm, 0.36-0.9mm, and 0.17-0.64mm.

4. The method for manufacturing high corrosion-resistant low-alloy steel according to claim 1, characterized in that, In S6, the hot-rolled steel strip coiling temperature is controlled at 570℃-610℃ during the hot-rolled steel strip coiling process.

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