900mpa grade high strength high corrosion resistant steel and method of manufacturing the same

Abstract

This invention discloses a 900MPa grade high-strength, high-corrosion-resistant steel for photovoltaic brackets and its manufacturing method, solving the technical problems of low strength, poor corrosion resistance, and low production efficiency of existing products. The composition of this high-strength, high-corrosion-resistant steel, by mass percentage, includes: C: 0.08%-0.10%, Si: 0.31%-0.40%, Mn: 0.91%-1.00%, P: 0.096%-0.105%, S: 0.0081%-0.0090%, Cu: 0.16%-0.26%, Cr: 5.2%-5.3%, Mo: 0.62%-0.71%, with the remainder being Fe and unavoidable impurities. The high-strength, high-corrosion-resistant steel meets the requirement of 6.913 ≤ MPF ≤ 7.185. The manufacturing method of the high-strength, high-corrosion-resistant steel includes smelting, continuous casting, hot charging of the continuously cast billet, heating, heat preservation, rough rolling, finish rolling, laminar flow cooling, coiling, and slow cooling in a slow cooling pit. This invention can improve the strength and corrosion resistance of steel and increase production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of hot-rolled steel strip manufacturing technology, specifically relating to a 900MPa grade high-strength, high-corrosion-resistant steel and its manufacturing method. Background Technology

[0002] Guided by the goals of dual carbon and energy transition, both domestic and international countries attach great importance to the development of renewable energy. Solar energy is the most abundant, safest, and cleanest renewable energy source. Since 2006, the global installed capacity of solar photovoltaic power has been on the rise, showing strong momentum.

[0003] Photovoltaic (PV) mounting systems are specialized structures designed for installing and securing solar cell modules in photovoltaic (PV) power generation systems. Due to scarce land resources, deserts, Gobi, wastelands, saline-alkali land, tidal flats, nearshore areas, and coal and oil mining subsidence areas are becoming the primary sites for PV power plants. In these harsh environments and open spaces, PV mounting systems are constantly exposed to wind, rain, snow, strong sunlight, and extreme temperatures, and bear their own weight, wind loads, snow loads, and seismic loads. To ensure the long-term stable and reliable operation of PV mounting systems in these harsh environments, the steel used in them must possess high strength and excellent corrosion resistance, meeting requirements for tensile strength, compressive strength, seismic resistance, sand erosion resistance, and corrosion resistance.

[0004] Currently, photovoltaic (PV) mounting systems primarily use ordinary Q235B or Q355B hot-dip galvanized steel sheets, which have low strength and are structurally heavy. Furthermore, hot-dip galvanizing severely pollutes the environment and harms the health of operators. In addition, PV mounting modules made from hot-dip galvanized steel sheets are easily damaged by impacts and scratches during transportation and installation, leading to the galvanized layer peeling off and resulting in high maintenance costs later on.

[0005] Weathering steel has unique corrosion resistance, high cost performance and environmental friendliness, making it an ideal material for manufacturing photovoltaic brackets. However, the strength and corrosion resistance of existing weathering steel cannot fully meet the service and economic requirements of photovoltaic brackets, especially the requirement for paint-free use in C5 environment. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a 900MPa grade high-strength, high-corrosion-resistant steel for photovoltaic brackets and a manufacturing method thereof, which can improve the strength and corrosion resistance of the steel, achieve lightweight and long service life, and at the same time reduce the production difficulty of photovoltaic brackets and improve production efficiency.

[0007] In a first aspect, the present invention provides a high-strength, high-corrosion-resistant steel for photovoltaic brackets, wherein the composition of the high-strength, high-corrosion-resistant steel comprises, by mass percentage: C: 0.08%-0.10%, Si: 0.31%-0.40%, Mn: 0.91%-1.00%, P: 0.096%-0.105%, S: 0.0081%-0.0090%, Cu: 0.16%-0.26%, Cr: 5.2%-5.3%, Mo: 0.62%-0.71%, with the remainder being Fe and unavoidable impurities.

[0008] The high-strength, high-corrosion-resistant steel meets the condition 6.913≤MPF≤7.185, where MPF is the mechanical property factor (abbreviation for Mechanical Property Factor), and its calculation formula is MPF=C%+0.12Si%+0.10Mn%+0.51P%+1.13Cr%+1.26Mo%.

[0009] Optionally, the high-strength, high-corrosion-resistant steel has the following properties: Yield strength ≥790MPa, tensile strength ≥900MPa, elongation after fracture ≥14%, and pass the cold bending test at 180°d=0; According to the GB / T10125-2021 standard "Artificial Atmosphere Corrosion Test - Salt Spray Test", the corrosion rate after a 720-hour neutral salt spray test using a NaCl solution with a concentration of 50 g / L ± 5 g / L is ≤1.715 g / (m²). 2 ·h), the corrosion rate is ≤71% compared to ordinary Q355B steel; The uniform corrosion rate on a single surface is ≤0.216mm after 25 years of uncoated service in a C5 environment.

[0010] Secondly, the present invention provides a method for manufacturing high-strength, high-corrosion-resistant steel for photovoltaic brackets, comprising the following steps: S1, through hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining, RH refining and slab continuous casting, to obtain a continuously cast billet with a thickness of 180-230mm; S2, the continuously cast billet is heated and charged into the 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; S7, hot-rolled steel coils are hot-loaded into the slow-cooling pit for slow cooling.

[0011] Optionally, in S2, the charging temperature of the continuously cast billet is controlled at 460-805℃.

[0012] Optionally, in S2, the continuous casting billet tapping temperature is controlled at 1220-1240℃ and the cumulative furnace dwell time is controlled at 200-230 minutes.

[0013] Optionally, in S3, the continuously cast billet is rough rolled in 7 passes, and the rough rolling start temperature is controlled at 1115-1135℃ and the rough rolling finish temperature is controlled at 1070-1090℃.

[0014] Optionally, in S3, the absolute reduction of the seven roughing passes is controlled as follows: 35.8-38.0 mm, 32.7-34.9 mm, 28.9-33.2 mm, 28.4-31.3 mm, 23.9-27.0 mm, 21.9-25.5 mm, and 21.1-24.3 mm, and the strip thickness is controlled as 30-42 mm.

[0015] Optionally, in S4, the strip is finished rolled by a 7-stand finishing mill, and the starting temperature of finishing rolling is controlled at 1020-1040℃ and the finishing rolling temperature is controlled at 870-890℃.

[0016] Optionally, in S4, the absolute reduction of the finishing mill 7 stands is controlled sequentially as follows: 14.19-18.52mm, 5.64-8.84mm, 2.34-4.37mm, 1.19-2.37mm, 0.72-1.42mm, 0.29-0.83mm, 0.11-0.58mm, and the thickness of the hot-rolled steel strip is controlled as 1.5-4.0mm.

[0017] Optionally, in S5, the hot-rolled steel strip is cooled in two stages on the laminar flow cooling roller table. The cooling rate of the first stage is controlled at 43.2-69.6℃ / s, and the temperature after the first stage cooling is 573-586℃. The cooling rate of the second stage is 0.8-3.1℃ / s.

[0018] Optionally, in S6, the hot-rolled steel strip winding temperature is controlled at 560-580℃ during the hot-rolled steel strip winding process.

[0019] Optionally, in S7, the hot-rolled steel coil is hot-loaded into a slow-cooling pit for slow cooling, and the surface temperature of the steel coil is controlled to be ≥335℃ when it is loaded into the slow-cooling pit, with a slow cooling time of 48-52 hours.

[0020] As can be seen from the above technical solution, the high-strength, high-corrosion-resistant steel for photovoltaic brackets and its manufacturing method provided by the present invention have the following advantages: This high-strength, high-corrosion-resistant steel boasts high strength, and can reduce weight by 38% and 25% respectively when replacing Q235B and Q355B galvanized sheets, demonstrating significant weight reduction. It also exhibits high corrosion resistance; according to GB / T10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test" standard, after a 720-hour neutral salt spray test using a NaCl solution with a concentration of 50 g / L ± 5 g / L, the corrosion rate is ≤1.715 g / (m³). 2 The corrosion rate of Q355B ordinary steel is ≤71% (·h); the uniform corrosion amount on one side is ≤0.216mm after 25 years of uncoated service in C5 environment.

[0021] Meanwhile, this high-strength, high-corrosion-resistant steel contains no Al and has a low content of the precious alloying element Cu, making smelting and continuous casting easier, steel easier to manufacture, and steel mills more efficient.

[0022] In addition, the high-strength and high-corrosion-resistant steel has a narrow range of C, Si, Mn, P, S, Cr, Cu, and Mo content and a narrow range of process parameters. The hot-rolled steel strip has stable mechanical properties, which can avoid photovoltaic bracket manufacturers from frequently adjusting process parameters due to fluctuations in the mechanical properties of raw materials. This results in high processing efficiency and low processing costs.

[0023] Furthermore, this high-strength, high-corrosion-resistant steel does not contain precious alloying elements such as Ni, Nb, and V, effectively reducing alloy costs. At the same time, photovoltaic brackets made from this high-strength, high-corrosion-resistant steel require no subsequent acid pickling, painting, or maintenance, offering advantages such as energy saving, environmental friendliness, short delivery cycles, and low operating costs.

[0024] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0025] 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.

[0026] Figure 1 This is a flowchart illustrating the manufacturing method of high-strength, high-corrosion-resistant steel in an embodiment of the present invention. Figure 2 This is a schematic diagram of a high-strength, high-corrosion-resistant steel sample that passed the 180°d=0 cold bending test in an embodiment of the present invention. Detailed Implementation

[0027] 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.

[0028] like Figure 1 , Figure 2 The illustration shows an embodiment of the present invention, which discloses a high-strength, high-corrosion-resistant steel for photovoltaic brackets. Its composition, by mass percentage, includes: C: 0.08%-0.10%, Si: 0.31%-0.40%, Mn: 0.91%-1.00%, P: 0.096%-0.105%, S: 0.0081%-0.0090%, Cu: 0.16%-0.26%, Cr: 5.2%-5.3%, Mo: 0.62%-0.71%, with the remainder being Fe and unavoidable impurities. Furthermore, the high-strength, high-corrosion-resistant steel satisfies 6.913 ≤ MPF ≤ 7.185, where MPF is the mechanical property factor, calculated using the formula: MPF = C% + 0.12Si% + 0.10Mn% + 0.51P% + 1.13Cr% + 1.26Mo.

[0029] The reasons for limiting the chemical elements in this embodiment are as follows: 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 900 MPa for the steel strip in this embodiment, and considering processing performance, weldability, and corrosion resistance while also maintaining economic efficiency, this invention controls the C content within the range of 0.08%-0.10%.

[0030] Si is not a precious alloying element. Practical experience has shown that Si has a higher solid solution strengthening coefficient in ferrite than 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 900 MPa for the steel strip of this invention, and considering processing performance, weldability, and corrosion resistance while also being economical, the Si content is controlled within the range of 0.31%-0.40%.

[0031] 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, increasing the ferrite nucleation rate, and reducing grain growth rate—in other words, refining the grain size. However, increasing the Mn content increases the carbon equivalent in the steel, which is detrimental to weldability. To achieve a tensile strength of over 900 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 0.91%-1.00%.

[0032] Practice has shown that phosphorus (P) has the second-highest solid solution strengthening effect in steel after carbon (C), and it can effectively improve the atmospheric corrosion resistance of steel. Among many alloying elements that improve corrosion resistance, P is the most cost-effective. 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 adversely affects the formability of the steel. To achieve a tensile strength of over 900 MPa in the steel strip of this invention, and considering processing performance, weldability, and corrosion resistance, while also taking into account economic efficiency, the P content of this invention is controlled within the range of 0.096%-0.105%.

[0033] Practice has shown that high sulfur (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. S is detrimental to the corrosion resistance of steel, and sulfides in steel can become sources of rust. Therefore, the S content should be reduced as much as possible. However, if the S content is controlled too low, it will increase manufacturing costs and reduce production efficiency. Considering the uniformity of mechanical properties, processing performance, and corrosion resistance of the high-strength, high-corrosion-resistant steel strip of this invention, while also taking into account economy and production efficiency, this invention controls the S content in the range of 0.0081%-0.0090%.

[0034] Practical experience has shown that Cu can form precipitates on the surface of steel, acting as a cathode to cause anodic passivation of the steel surface, and accumulating in the rust layer, altering the rust layer structure and inhibiting Cl... - Cu penetrates the matrix, making it an effective element for 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 increases product costs. Considering the hot working performance, surface quality, and corrosion resistance of the steel strip in this invention, while also taking into account economic efficiency, this invention controls the Cu content within the range of 0.16%-0.26%.

[0035] 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, prevent the corrosive medium from further penetrating 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 plasticity of the steel, worsening its formability and weldability, and increasing the cost of the alloy. In order to achieve a tensile strength of over 900 MPa for the steel strip of this invention, and considering corrosion resistance, plasticity, processing performance, weldability, and economic efficiency, the Cr content of this invention is controlled within the range of 5.2%-5.3%.

[0036] Practice has shown that Mo has a strong tendency to agglomerate in steel. The resulting solute dragging and reduced diffusion of C atoms at the interface front jointly delay the proeutectoid ferrite transformation, promote bainite formation, and improve the steel's strength and toughness. In the rust layer of low-alloy corrosion-resistant steel, Mo usually exists as hexavalent molybdate, and in more acidic environments, as the more stable MoO3. These compounds make the rust layer more compact, dense, and complete, improving the steel's corrosion resistance. When Mo is added together with other corrosion-resistant elements, it can better exert a synergistic effect, especially when the steel contains a high amount of Cr, Mo can enhance the corrosion resistance of Cr. However, excessively high Mo content will worsen the steel's formability and weldability, and increase alloy costs. To achieve a tensile strength of over 900 MPa in the steel strip of this invention, and considering its corrosion resistance, processing performance, and economy, while fully leveraging the synergistic effect of Cr and Mo in improving the steel's corrosion resistance, the Mo content in this invention is controlled within the range of 0.62%-0.71%.

[0037] Practical experience has shown that the mechanical property factor (MPF) of the high-strength, high-corrosion-resistant steel of this invention has a significant impact on the matching of the finished product's strength, plasticity, and formability. The MPF calculation formula is MPF = C% + 0.12Si% + 0.10Mn% + 0.51P% + 1.13Cr% + 1.26Mo%. When MPF ​​< 6.913, although the high-strength, high-corrosion-resistant steel of this invention has a high elongation after fracture and good formability, its yield strength and tensile strength are low, which cannot meet the technical requirements and the safe service requirements of photovoltaic brackets. When MPF ​​> 7.185, although the high-strength, high-corrosion-resistant steel of this invention has a high yield strength and tensile strength, its elongation after fracture is low, and its formability is poor, which cannot meet the technical requirements and the processing requirements of photovoltaic brackets. To achieve the optimal matching of the yield strength, tensile strength, elongation after fracture, and formability of this high-strength, high-corrosion-resistant steel, while simultaneously meeting the technical requirements and the processing and safe service requirements of photovoltaic brackets, the embodiments of this invention control 6.913 ≤ MPF ≤ 7.185.

[0038] In this embodiment, the selection of C, Si, Mn, P, Cr, Mo and MPF has a synergistic effect. By controlling the content of each element and MPF 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-strength and high-corrosion-resistant steel for photovoltaic brackets has both high strength and excellent cold working performance.

[0039] Secondly, the selection of the contents of the above-mentioned elements Si, P, S, Cu, Cr and Mo 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, so that the high-strength and high-corrosion-resistant steel has high corrosion resistance, eliminating the need for subsequent pickling, painting and maintenance, and saving energy and protecting the environment.

[0040] Meanwhile, the selection of C, Mn, S, and Cu has a synergistic effect. By controlling the content of each element within the above range, defects such as hot-rolled network cracks can be avoided. This gives the high-strength and high-corrosion-resistant steel for photovoltaic brackets excellent hot working performance and high surface quality, making it easier to process, more efficient to produce, cheaper to manufacture, and faster to deliver. This meets the stringent processing and service requirements of photovoltaic brackets.

[0041] The high-strength, high-corrosion-resistant steel in this embodiment has at least the following properties: (1) Yield strength ≥790MPa, tensile strength ≥900MPa, elongation after fracture ≥14%, and pass the cold bending test at 180°d=0.

[0042] (2) According to GB / T10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test" standard, the corrosion rate after 720 hours of neutral salt spray test using a NaCl solution with a concentration of 50 g / L ± 5 g / L is ≤1.715 g / (m²). 2 The corrosion rate of Q355B ordinary steel is ≤71% (·h).

[0043] (3) The uniform corrosion amount on one side is ≤0.216mm after 25 years of uncoated service in C5 environment.

[0044] like Figure 1 As shown, this embodiment also discloses a method for manufacturing high-strength, high-corrosion-resistant steel for photovoltaic brackets, including the following steps: S1 is obtained by hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining, RH refining and slab continuous casting. S2, the continuously cast billet is heated and charged into the 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, the hot-rolled steel strip is wound into hot-rolled steel coils by a coiler.

[0045] S7, hot-rolled steel coils are hot-loaded into the slow-cooling pit for slow cooling.

[0046] In S1, the composition of the continuously cast billet by mass percentage is as follows: C: 0.08%-0.10%, Si: 0.31%-0.40%, Mn: 0.91%-1.00%, P: 0.096%-0.105%, S: 0.0081%-0.0090%, Cu: 0.16%-0.26%, Cr: 5.2%-5.3%, Mo: 0.62%-0.71%, with the remainder being Fe and unavoidable impurities. Furthermore, the MPF in the continuously cast billet is 6.913 ≤ MPF ≤ 7.185, where MPF is the mechanical property factor, calculated using the formula: MPF = C% + 0.12Si% + 0.10Mn% + 0.51P% + 1.13Cr% + 1.26Mo.

[0047] In S1, the thickness of the continuously cast billet is 180-230mm. Practical experience has shown that, given a fixed width and length, 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 coiler. Therefore, considering all these factors, this embodiment controls the billet thickness to 180-230mm.

[0048] In S2, the charging temperature of the continuously cast billet is controlled between 460-805℃. Practical experience has shown that if the charging temperature is <460℃, energy consumption and oxidation loss increase, and the tendency for cracking due to thermal and structural stress in the billet is enhanced. When the charging temperature is ≥460℃, energy consumption and oxidation loss are significantly reduced, while cracking defects in the billet are avoided. If the charging temperature is >805℃, the steelmaking and continuous casting capacities cannot meet the hot rolling requirements, making integrated, continuous production of metallurgy, casting, and rolling impossible. When the charging temperature is ≤805℃, the steelmaking, continuous casting, and hot rolling capacities are well-matched, allowing for stable integrated, continuous production of metallurgy, casting, and rolling. Therefore, this invention controls the charging temperature of the continuously cast billet to 460-805℃.

[0049] In S2, the continuous casting billet tapping temperature is controlled at 1220-1240℃. Practical experience has shown that if the tapping temperature is below 1220℃, although the austenite grains are refined, the billet exhibits poor thermoplasticity, high deformation resistance, difficulty in hot deformation, and low mill operating rate. If the tapping temperature is above 1240℃, while the billet's thermoplasticity increases, deformation resistance decreases, and it is more prone to hot deformation, resulting in a high mill operating rate, the austenite grains tend to coarsen. Therefore, considering all these factors, this invention controls the tapping temperature of the continuous casting billet to 1220-1240℃.

[0050] In S2, the cumulative furnace dwell time of the continuously cast billet is controlled at 200-230 minutes. Practical experience has shown that, under the unique composition system of the high-strength, high-corrosion-resistant steel of this invention, if the cumulative furnace dwell time of the continuously cast billet is less than 200 minutes, its microstructure is difficult to homogenize, rolling energy consumption is high, and equipment accidents are prone to occur; if the cumulative furnace dwell time is longer than 230 minutes, oxidation loss, decarburization, and energy consumption increase, while the mill operating rate and production efficiency decrease. Therefore, considering the above effects, this invention determines the cumulative furnace dwell time of the continuously cast billet to be 200-230 minutes.

[0051] In S3, the continuously cast billet is rough-rolled through 7 passes, with the initial rough-rolling temperature controlled at 1115-1135℃ and the final rough-rolling temperature at 1070-1090℃. Practice has shown that 7 passes of rough rolling better balance product quality and yield. The main metallurgical purpose of rough rolling is to disrupt the as-cast structure of the continuously cast billet, effectively refining the austenite grains through multiple recrystallizations to obtain a uniform and fine austenite structure. If the initial rough-rolling 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 initial rough-rolling temperature is too low, the strip shape control becomes more difficult, increasing the mill load and rolling energy consumption, which is detrimental to smooth rolling. Therefore, considering all these factors, this invention determines the number of rough-rolling passes to be 7, with an initial rough-rolling temperature of 1115-1135℃ and a final rough-rolling temperature of 1070-1090℃.

[0052] In S3, the absolute reduction for the seven roughing passes is controlled as follows: 35.8-38.0 mm, 32.7-34.9 mm, 28.9-33.2 mm, 28.4-31.3 mm, 23.9-27.0 mm, 21.9-25.5 mm, and 21.1-24.3 mm, with the strip thickness controlled at 30-42 mm. Practical experience has shown that if the absolute reduction in roughing is too small, grain inhomogeneity will occur, reducing plasticity; if the absolute reduction is too large, it will not only increase the deformation resistance and load of the roughing roll, but also cause curling and, in severe cases, "roll wrapping" accidents, leading to equipment hazards. If the strip is too thick, the cumulative reduction rate and pass reduction rate of roughing will decrease, making partial recrystallization more likely and causing mixed crystal phenomena. This will adversely affect the uniformity of the mechanical properties of the finished steel strip, while also increasing the rolling load and energy consumption of the finishing mill, affecting the stability of finishing. If the strip is too thin, it will be detrimental to improving the strip shape quality, and will also increase the rolling load and energy consumption of the roughing mill, hindering smooth rolling. Furthermore, it will be impossible to guarantee the finishing mill opening temperature required for rolling the thin-gauge finished steel strip of this invention, and may even increase the rolling load and energy consumption of the finishing mill. Therefore, considering the above effects, the absolute reduction for the seven passes of roughing is determined to be: 35.8-38.0 mm, 32.7-34.9 mm, 28.9-33.2 mm, 28.4-31.3 mm, 23.9-27.0 mm, 21.9-25.5 mm, and 21.1-24.3 mm, with a strip thickness of 30-42 mm.

[0053] In S4, the strip is finished rolled using a 7-stand finishing mill, with the initial finishing temperature controlled at 1020-1040℃ and the final finishing temperature at 870-890℃. Practical experience has shown that if the initial finishing temperature is too high, partial recrystallization easily occurs in the F1 and F2 finishing mill stands, leading to mixed crystal formation, differences in the microstructure of the finished steel strip, and abnormal fluctuations in mechanical properties. If the initial finishing temperature is too low, the desired final finishing temperature cannot be guaranteed. If the final finishing temperature is too high, the microstructure of the finished steel strip will coarsen, and the strength will decrease; if the final finishing temperature is too low, the strength of the finished steel strip will increase, but the plasticity and formability will decrease, resulting in an unreasonable match of overall mechanical properties. 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, it can lead to scrapped steel strip and equipment damage. Considering all these factors, this invention controls the initial finishing temperature at 1020-1040℃ and the final finishing temperature at 870-890℃.

[0054] In S4, the absolute reduction of the 7 stands in the finishing mill is controlled as follows: 14.19-18.52mm, 5.64-8.84mm, 2.34-4.37mm, 1.19-2.37mm, 0.72-1.42mm, 0.29-0.83mm, and 0.11-0.58mm, with the hot-rolled strip thickness controlled at 1.5-4.0mm. The use of a 7-stand finishing mill depends on the actual equipment configuration. Practice has shown that if the absolute reduction of each stand in the finishing mill is too small, grain inhomogeneity will occur, reducing plasticity; if the absolute reduction is too large, the deformation resistance and load of each stand in the finishing mill will increase, leading to potential equipment hazards. The finished strip thickness of 1.5-4.0mm is selected by the user. Taking all the above factors into consideration, the absolute reduction of each stand in the 7-stand finishing mill is determined to be 14.19-18.52mm, 5.64-8.84mm, 2.34-4.37mm, 1.19-2.37mm, 0.72-1.42mm, 0.29-0.83mm, and 0.11-0.58mm respectively, with a hot-rolled steel strip thickness of 1.5-4.0mm.

[0055] In S5, the hot-rolled steel strip is cooled in two stages on the laminar flow cooling roller conveyor. The cooling rate of the first stage is controlled at 43.2-69.6℃ / s, and the temperature after the first stage is 573-586℃. The cooling rate of the second stage is 0.8-3.1℃ / s. Practice has shown that, under the unique composition system of the high-strength, high-corrosion-resistant steel strip of this invention, the above-mentioned cooling method and process parameters are beneficial for optimizing the cooling path, refining ferrite grains, and achieving a good match between the strength, plasticity, and cold forming performance of the finished steel strip. Based on these advantages, the cooling method for the hot-rolled steel strip on the laminar flow cooling roller conveyor of this invention is determined to be two-stage cooling, with the cooling rate of the first stage controlled at 43.2-69.6℃ / s, the temperature after the first stage being 573-586℃, and the cooling rate of the second stage being 0.8-3.1℃ / s.

[0056] In S6, the hot-rolled steel strip coiling temperature is controlled at 560-580℃ during the coiling process. Practical experience has shown that by rationally 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 smaller than ferrite grains, approximately 1μm, and have a higher dislocation density, thus improving the overall mechanical properties of the steel strip. Furthermore, rationally controlling the coiling temperature is also a necessary measure to reduce the difficulty of sheet and coil shape control. Considering all these factors, the coiling temperature of this invention is determined to be 560-580℃.

[0057] In S7, the hot-rolled steel coil is hot-loaded into a slow-cooling pit for slow cooling, with the surface temperature of the coil controlled to be ≥335℃ upon loading into the pit, and the slow cooling time to be 48-52 hours. Practice has shown that during laminar flow cooling, the steel strip experiences significant internal stress due to phase transformation, which is detrimental to improving the finished product's shape quality. During coiling, the head of the steel strip directly contacts the coil drum, while the tail is exposed to air. The cooling rates at the head and tail are significantly higher than those inside the coil, leading to differences in microstructure and fluctuations in mechanical properties across different parts of the steel strip. To compensate for these shortcomings, this embodiment of the invention hot-rolled steel coil is hot-loaded into a slow-cooling pit after coiling. If the temperature of the steel coil entering the slow-cooling pit is below 335℃ and the slow cooling time is less than 48 hours, the effect of releasing internal stress and improving microstructure uniformity is poor. If the slow cooling time is longer than 52 hours, production efficiency is reduced. Considering all these factors, this embodiment of the invention determines that the surface temperature of the steel coil must be ≥335℃ when loading into the slow-cooling pit, and the slow cooling time must be 48-52 hours.

[0058] The present invention is further illustrated below by way of examples, but the invention is not limited to the scope of the examples. Experimental methods not specifically described in the following examples were performed using conventional methods and conditions.

[0059] Examples 1-3: The preparation methods of Examples 1-3 of this invention include the following steps: First, continuous casting billets are obtained through hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining, RH refining and slab continuous casting. The chemical composition and MPF of the continuous casting billets obtained in Examples 1 to 3 are shown in Table 1.

[0060] Secondly, the continuously cast billet is hot-charged, heated, rough-rolled, finish-rolled, and cooled to obtain hot-rolled steel strip, which is then coiled to obtain hot-rolled steel coil. The hot-rolled steel coil is hot-charged into a slow cooling pit for slow cooling. The process parameters for each process are shown in Tables 2, 3, 4, and 5, and the properties of the obtained steel coil are shown in Table 6.

[0061] Table 1 Chemical composition (mass percentage) and MPF of embodiments of the present invention

[0062] Table 2. Loading and heating process parameters of embodiments of the present invention.

[0063] Table 3. Roughing process parameters of embodiments of the present invention

[0064] Table 4 Finishing rolling process parameters of embodiments of the present invention

[0065] Table 5 Cooling process parameters of embodiments of the present invention

[0066] Table 6 Performance table of steel coils according to embodiments of the present invention

[0067] As shown in Tables 1-6, the embodiments of the present invention differ significantly from those of general weathering steel in terms of chemical composition, furnace loading, heating, rough rolling, finish rolling, cooling, and other process parameters. This results in significant differences in various properties. The high-strength, high-corrosion-resistant 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.

[0068] As can be seen from the above process, the high-strength and high-corrosion-resistant steel and its manufacturing method in this invention optimize the design of the content of elements such as C, Si, Mn, P, Cr, and Mo, the mechanical property factor (MPF), and give full play to their synergistic effect. By controlling the continuous casting billet charging temperature, tapping temperature, furnace dwell time, roughing rolling start and finish rolling temperatures, roughing rolling passes, absolute reduction of each roughing rolling pass, strip thickness, finishing rolling start and finish rolling temperatures, finishing rolling passes, absolute reduction of each finishing rolling stand, finished product thickness, cooling method, first stage cooling rate, temperature after first stage cooling, second stage cooling rate, and coiling temperature, the finished steel has a yield strength ≥790MPa, tensile strength ≥900MPa, elongation after fracture ≥14%, and passes the 180°d=0 cold bending test.

[0069] The high-strength, high-corrosion-resistant steel and its manufacturing method of this invention optimize the content of elements such as Si, P, S, Cu, Cr, and Mo, fully leveraging their synergistic effects. By controlling the series of process parameters including furnace loading, heating, rough rolling, finish rolling, and cooling, the finished steel achieves a corrosion rate ≤1.715 g / (m²) after a 720-hour neutral salt spray test using a 50 g / L ± 5 g / L NaCl solution, according to the GB / T10125-2021 standard for "Artificial Atmosphere Corrosion Test - Salt Spray Test". 2 The corrosion rate of Q355B ordinary steel is ≤71% (·h); the uniform corrosion amount on one side is ≤0.216mm after 25 years of uncoated service in C5 environment.

[0070] The high-strength, high-corrosion-resistant steel in this invention has high strength and can reduce weight by 38% and 25% respectively compared to Q235B and Q355B galvanized steel sheets, resulting in significant weight reduction. This high-strength, high-corrosion-resistant steel also exhibits strong corrosion resistance, meeting the long-life service requirements of photovoltaic brackets.

[0071] Meanwhile, by optimizing the content of C, Mn, S, and Cu elements in the high-strength and high-corrosion-resistant steel and giving full play to their synergistic effects, and by controlling the series of process parameters such as furnace charging, heating, rough rolling, finish rolling, and cooling, defects such as hot-rolled network cracks can be avoided. This gives the high-strength and high-corrosion-resistant steel excellent hot working performance and high surface quality, making it easier to smelt, continuously cast, and hot-roll, thus reducing manufacturing difficulty, increasing production efficiency, lower manufacturing costs, and shortening delivery cycles.

[0072] In addition, the high-strength and high-corrosion-resistant steel has a narrow range of control over the content of C, Si, Mn, P, S, Cr, Cu, and Mo elements, as well as a series of process parameters such as furnace loading, heating, rough rolling, finish rolling, and cooling. The hot-rolled steel strip has stable mechanical properties, which can avoid photovoltaic bracket manufacturers from frequently adjusting process parameters due to fluctuations in the mechanical properties of raw materials. This results in high processing efficiency and low processing costs.

[0073] Furthermore, this high-strength, high-corrosion-resistant steel contains no Al, Ni, Nb, V, or other precious alloying elements, effectively reducing alloy costs. Simultaneously, photovoltaic brackets made from this high-strength, high-corrosion-resistant steel require no subsequent acid pickling, painting, or maintenance, offering advantages such as energy saving, environmental friendliness, and low operating costs.

[0074] 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.

[0075] 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.

[0076] 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 900MPa grade high-strength, high-corrosion-resistant steel for photovoltaic brackets, characterized in that, The composition of the high-strength, high-corrosion-resistant steel by mass percentage includes: C: 0.08%-0.10%, Si: 0.31%-0.40%, Mn: 0.91%-1.00%, P: 0.096%-0.105%, S: 0.0081%-0.0090%, Cu: 0.16%-0.26%, Cr: 5.2%-5.3%, Mo: 0.62%-0.71%, with the remainder being Fe and unavoidable impurities; The high-strength, high-corrosion-resistant steel meets the condition 6.913≤MPF≤7.185, where MPF is the mechanical property factor, and its calculation formula is MPF=C%+0.12Si%+0.10Mn%+0.51P%+1.13Cr%+1.26Mo%.

2. The high-strength, high-corrosion-resistant steel according to claim 1, characterized in that, The high-strength, high-corrosion-resistant steel has the following properties: Yield strength ≥790MPa, tensile strength ≥900MPa, elongation after fracture ≥14%, and pass the cold bending test at 180°d=0. According to the GB / T10125-2021 standard "Artificial Atmosphere Corrosion Test - Salt Spray Test", the corrosion rate after a 720-hour neutral salt spray test using a NaCl solution with a concentration of 50 g / L ± 5 g / L is ≤1.715 g / (m²). 2 ·h), the corrosion rate is ≤71% compared to ordinary Q355B steel; The uniform corrosion rate on a single surface is ≤0.216mm after 25 years of uncoated service in a C5 environment.

3. A method for manufacturing high-strength, high-corrosion-resistant steel according to claim 1 or 2, characterized in that, Includes the following steps: S1, through hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining, RH refining and slab continuous casting, to obtain a continuously cast billet with a thickness of 180-230mm; S2, the continuously cast billet is heated and charged into the 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; S7, hot-rolled steel coils are hot-loaded into the slow-cooling pit for slow cooling.

4. The method for manufacturing high-strength, high-corrosion-resistant steel according to claim 3, characterized in that, In S2, the charging temperature of the continuous casting billet is controlled at 460-805℃; in S2, the unloading temperature of the continuous casting billet is controlled at 1220-1240℃, and the cumulative furnace dwell time is 200-230 minutes.

5. The method for manufacturing high-strength, high-corrosion-resistant steel according to claim 3, characterized in that, In S3, the continuously cast billet is rough rolled in 7 passes, and the rough rolling start temperature is controlled at 1115-1135℃ and the rough rolling finish temperature is controlled at 1070-1090℃.

6. The method for manufacturing high-strength, high-corrosion-resistant steel according to claim 5, characterized in that, In S3, the absolute reduction of the seven roughing passes is controlled as follows: 35.8-38.0mm, 32.7-34.9mm, 28.9-33.2mm, 28.4-31.3mm, 23.9-27.0mm, 21.9-25.5mm, and 21.1-24.3mm, and the strip thickness is controlled as 30-42mm.

7. The method for manufacturing high-strength, high-corrosion-resistant steel according to claim 3, characterized in that, In S4, the strip is finished rolled using a 7-stand finishing mill, with the initial finishing temperature controlled at 1020-1040℃ and the final finishing temperature at 870-890℃. The absolute reduction of the 7 stands is controlled as follows: 14.19-18.52mm, 5.64-8.84mm, 2.34-4.37mm, 1.19-2.37mm, 0.72-1.42mm, 0.29-0.83mm, and 0.11-0.58mm, and the hot-rolled strip thickness is controlled at 1.5-4.0mm.

8. The method for manufacturing high-strength, high-corrosion-resistant steel according to claim 3, characterized in that, In S5, the hot-rolled steel strip is cooled in two stages on the laminar flow cooling roller table. The cooling rate of the first stage is controlled at 43.2-69.6℃ / s, and the temperature after the first stage cooling is 573-586℃. The cooling rate of the second stage is 0.8-3.1℃ / s.

9. The method for manufacturing high-strength, high-corrosion-resistant steel according to claim 3, characterized in that, In S6, the hot-rolled steel strip coiling temperature is controlled at 560-580℃ during the hot-rolled steel strip coiling process.

10. The method for manufacturing high-strength, high-corrosion-resistant steel according to claim 3, characterized in that, In S7, hot-rolled steel coils are hot-loaded into a slow-cooling pit for slow cooling. The surface temperature of the steel coils is controlled to be ≥335℃ when they are loaded into the slow-cooling pit, and the slow cooling time is 48-52 hours.

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