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; obtaining a steel coil through the continuous casting blank; and the continuous casting blank comprises the following components in percentage by mass: C: 0.14%-0.16%, Si: 0.96%-1.10%, Mn: 0.21%-0.30%, P: 0.041%-0.055%, S: 0.0031%-0.0040%, Cu: 0.13%-0.18%, Cr: 3.4%-3.6%, Alt: 0.13%-0.16%, and the rest is Fe and inevitable impurities. The prepared steel coil can better meet the development requirements 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] In recent years, driven by the goals of dual-carbon and clean energy transformation, the development of renewable energy has been unstoppable. Solar energy, as a renewable energy source, has significant advantages such as being clean, safe, inexhaustible, and readily available. Photovoltaic power generation is a form of solar energy utilization and is the fastest-growing power generation technology. Its incremental power generation accounts for a steadily increasing proportion of the global incremental power generation.

[0003] Photovoltaic (PV) mounting systems are specialized equipment installed in photovoltaic (PV) power plants to support, fix, and rotate PV modules. They represent the most material-intensive link in the PV industry chain. On one hand, PV power plants are trending towards higher power outputs, increasing module weight and consequently raising the load on PV mounting systems. On the other hand, PV power generation is often carried out in harsh and variable environments such as deserts, Gobi, wastelands, and saline-alkali lands. Both of these factors necessitate that PV mounting systems possess high load-bearing capacity, corrosion resistance, and stability.

[0004] The raw materials for photovoltaic (PV) mounting systems include aluminum alloys, stainless steel, and hot-dip galvanized or zinc-aluminum-magnesium (ZAM) carbon steel. Aluminum alloys and stainless steel offer excellent corrosion resistance, but their high cost and low strength make them difficult to widely adopt. Currently, the main raw material for PV mounting systems is carbon steel as the base material, with hot-dip galvanizing or ZAM applied to improve corrosion resistance. However, hot-dip galvanizing or ZAM pollutes the environment, increases production steps, prolongs the process, and raises manufacturing costs. Furthermore, the coating is easily damaged during transportation, processing, and installation, leading to corrosion of the base material, requiring subsequent maintenance to prevent premature failure. Therefore, none of these three materials can meet the development requirements of high-strength, lightweight, environmentally friendly, and low-cost PV mounting systems.

[0005] Photovoltaic brackets made of weathering steel 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, photovoltaic brackets made of weathering steel offer advantages such as energy saving and environmental friendliness. To adapt to the development trend of photovoltaic power plants, weathering steel for photovoltaic brackets should simultaneously possess advantages such as high strength, lightweight, high corrosion resistance, long lifespan, ease of manufacturing, and low cost. Existing weathering steel products cannot yet fully meet these requirements.

[0006] Existing technology discloses a high-toughness 800MPa grade photovoltaic bracket steel with the following chemical composition: C: ≤0.08%, Si: 0.20%–0.40%, Mn: 0.50%–0.60%, P: ≤0.02%, S: ≤0.01%, Cu: 0.25%–0.30%, Cr: 2.5%–3.0%, Ti: 0.10%–0.15%, Als: 0.02%–0.05%, N: ≤0.0060%; the steel has a thickness of 1.5–6.0 mm, an I index of 8.07–8.96, a yield strength of 735–821 MPa, a tensile strength of 849–920 MPa, and an elongation after fracture of 18–24%. However, the above-mentioned photovoltaic bracket steel has a high content of the precious alloying element Cu, resulting in high product cost and a tendency to produce network crack defects during hot rolling. High Ti content leads to coarse TiN precipitates that easily become stress concentration points and microcrack initiations, consequently reducing the formability and fatigue performance of photovoltaic (PV) brackets. Furthermore, unstable Ti recovery rates result in large fluctuations in mechanical properties, increasing the processing difficulty of PV brackets and reducing processing efficiency. Additionally, the aforementioned PV bracket steels lack data on 5-year corrosion resistance, making material selection difficult for users.

[0007] The prior art discloses a low-cost 800MPa grade antimony-containing weathering steel for photovoltaic brackets. Its chemical composition includes: C: ≤0.08%, Si: 0.35%~0.50%, Mn: 0.40%~0.60%, P: 0.08%~0.12%, S: ≤0.010%, Cu: 0.25%~0.40%, Cr: 0.75%~1.00%, Ti: 0.120%~0.170%, N: ≤0.0040%, Sb: 0.05%~0.07%; and the steel has a thickness of 1.5~4.0mm, an I index of 7.61-9.02, a tensile strength of 850-875MPa, and an elongation after fracture of 23.5-24.5%. However, the high phosphorus (P) content in the aforementioned photovoltaic (PV) bracket steel leads to severe segregation in the cast billet, which consequently reduces the steel's plasticity, low-temperature toughness, and weldability. It also easily induces hydrogen-induced cracking, stress corrosion cracking, and surface cracking, exacerbating intergranular corrosion. Simultaneously, the high content of the precious alloying element copper (Cu) increases product cost and easily generates network crack defects during hot rolling. The high titanium (Ti) content results in coarse TiN precipitates that become stress concentration points and microcrack initiations, consequently reducing the formability and fatigue performance of the PV bracket. The unstable recovery rate of Ti leads to large fluctuations in mechanical properties, increasing the processing difficulty and reducing processing efficiency. Furthermore, sulfur (Sb) in the aforementioned PV bracket steel is one of the five major harmful elements. It easily causes segregation at the center of the cast billet and tends to agglomerate at grain boundaries, weakening grain boundaries and increasing the tendency for intergranular brittle fracture. This significantly reduces the steel's impact toughness and formability. It also tends to precipitate and accumulate between the steel matrix and oxide layer, increasing the tendency for hot brittleness and deteriorating the surface quality of the steel strip. Additionally, the aforementioned PV bracket steel lacks data on 25-year corrosion resistance, making material selection difficult for users.

[0008] The prior art also discloses a high weathering steel for photovoltaic brackets with a strength of 800MPa, the chemical composition of which includes: C: ≤0.08%, Si: 0.20%~0.30%, Mn: 0.40%~0.60%, P: ≤0.02%, S: ≤0.010%, Cu: 0.25%~0.40%, Cr: 2.50%~3.00%, Ni: 0.20%~0.40%, Nb: 0.015%~0.035%, Ti: 0.100%~0.150%, N: ≤0.0040%; and the steel has a thickness of 1.5mm~4.0mm, an I index of 8.3-9.79, a tensile strength of 855-895MPa, and an elongation after fracture of 23-25.5%. However, the steel used in photovoltaic brackets has a high content of the precious alloying element Cu, resulting in high product costs and a tendency to produce network crack defects during hot rolling. Furthermore, the addition of precious alloying elements such as Ni and Nb further increases the alloy cost. In addition, the high Ti content leads to coarse TiN precipitates that easily become stress concentration points and microcrack initiations, reducing the formability and fatigue performance of the photovoltaic bracket. The unstable Ti recovery rate results in large fluctuations in mechanical properties, which correspondingly increases the processing difficulty and reduces processing efficiency. Moreover, the aforementioned photovoltaic bracket steel lacks data on 25-year corrosion resistance, making material selection difficult for users. Summary of the Invention

[0009] 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 a long service life, high strength, and excellent corrosion resistance.

[0010] According to one aspect of the present invention, a method for manufacturing a steel coil for a photovoltaic support is provided, comprising:

[0011] Continuous casting billets are obtained through pretreatment;

[0012] The continuously cast billet is heated and held at a constant temperature.

[0013] The continuously cast billet is rough-rolled using a roughing mill to obtain a strip billet;

[0014] The strip is finished by a finishing mill to obtain hot-rolled steel strip; and

[0015] The hot-rolled steel strip is cooled and then coiled into a steel coil.

[0016] The continuously cast billet comprises the following components by mass percentage:

[0017] C: 0.14%-0.16%, Si: 0.96%-1.10%, Mn: 0.21%-0.30%, P: 0.041%-0.055%, S: 0.0031%-0.0040%, Cu: 0.13%-0.18%, Cr: 3.4%-3.6%, Alt: 0.13%-0.16%, with the remainder being Fe and unavoidable impurities.

[0018] Furthermore, the continuously cast billet also needs to satisfy C / Cu ≤ 1.2.

[0019] Furthermore, the process of obtaining the continuous casting billet through pretreatment specifically involves: obtaining the continuous casting billet through hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining, and slab continuous casting.

[0020] 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.

[0021] The continuous casting billet has a tapping temperature of 1170-1190℃ and a cumulative furnace dwell time of 180-210 minutes.

[0022] 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 1120-1140℃ and the final rolling temperature of the roughing mill to be 1050-1090℃, and using a roughing mill to roll the continuously cast billet to obtain a strip billet.

[0023] The thickness of the strip obtained from rough rolling is 28-40 mm. The rough rolling process consists of 7 passes, with the following process parameters for each pass: 1.8-2.2 m / s for the first pass, 2.4-2.8 m / s for the second pass, 3.3-3.7 m / s for the third pass, 3.8-4.2 m / s for the fourth pass, 3.8-4.2 m / s for the fifth pass, 4.8-5.2 m / s for the sixth pass, and 5.3-5.7 m / s for the seventh pass.

[0024] 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 990-1040℃ and the final rolling temperature of the finishing mill to be 840-880℃, and using a finishing mill to finish-roll the strip billet to obtain hot-rolled steel strip.

[0025] 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 process parameters of each stand are as follows: the rolling speed of the 1st stand is 0.96-1.26 m / s, the rolling speed of the 2nd stand is 1.63-2.34 m / s, the rolling speed of the 3rd stand is 2.5-3.82 m / s, the rolling speed of the 4th stand is 3.41-5.5 m / s, the rolling speed of the 5th stand is 4.26-7.37 m / s, the rolling speed of the 6th stand is 5.27-9.07 m / s, and the rolling speed of the 7th stand is 6.22-10.37 m / s.

[0026] 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:

[0027] 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. During the cooling process, the flow rate ratio of the cooling water in the upper and lower manifolds is 8:12. The coiling temperature is controlled at 530-570℃. The cooled hot-rolled steel strip is then coiled into a steel coil using a coiler.

[0028] After cooling the hot-rolled steel strip and coiling the cooled hot-rolled steel strip into a steel coil, the method further includes:

[0029] Within 15 minutes, the steel coil unloaded from the coiler is hoisted into a slow cooling pit for slow cooling, with the temperature of the steel coil entering the slow cooling pit being ≥480℃; and the steel coil is hoisted out of the slow cooling pit after 60-66 hours of slow cooling.

[0030] The present invention also provides a steel coil for photovoltaic brackets, which is prepared by any of the above-described preparation methods.

[0031] Furthermore, the yield strength is ≥690MPa, the tensile strength is ≥800MPa, the elongation after fracture is ≥18%, and the 180°d=a cold bending test is qualified;

[0032] The corrosion rate of the steel coil after cyclic immersion in a mixed solution of 0.01 mol / L NaHSO3 and 3.5% NaCl for 72 hours was ≤1.8 g / (m³). 2 •h); The uniform corrosion on one side of the steel coil after 25 years of uncoated service in C1, C2, C3 and C4 environments is ≤4μm, ≤12μm, ≤26μm and ≤45μm, respectively.

[0033] 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:

[0034] 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, low cost, high efficiency, no coating required, no maintenance, energy saving, and environmental protection. Attached Figure Description

[0035] 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.

[0036] 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, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart of the preparation method according to an embodiment of the present invention. Detailed Implementation

[0038] 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.

[0039] 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.

[0040] 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:

[0041] Step S001: Obtain the continuous casting billet through pretreatment;

[0042] Step S002: Heating and holding the continuously cast billet;

[0043] Step S003: The continuously cast billet is rough rolled using a roughing mill to obtain a strip billet;

[0044] Step S004: The strip is finished rolled using a finishing mill to obtain hot-rolled steel strip; and

[0045] Step S005: Cool the hot-rolled steel strip and then coil the cooled hot-rolled steel strip into a steel coil;

[0046] The continuously cast billet in step S001, by mass percentage, comprises the following components:

[0047] C: 0.14%-0.16%, Si: 0.96%-1.10%, Mn: 0.21%-0.30%, P: 0.041%-0.055%, S: 0.0031%-0.0040%, Cu: 0.13%-0.18%, Cr: 3.4%-3.6%, Alt: 0.13%-0.16%, with the remainder being Fe and unavoidable impurities.

[0048] The steel coils prepared using the method described in this invention have a long service life when used as photovoltaic supports, meeting the requirement of 25 years of service in C1-C4 environments.

[0049] The reasons for the limitations on the chemical elements in the embodiments of the present invention are as follows:

[0050] 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 corrosion resistance, ductility, toughness, weldability, and formability of the steel decrease. To ensure the steel strip of this invention has a long service life, and considering strength, weldability, and processability while also being economical, this invention controls the C content within the range of 0.14%-0.16%.

[0051] 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 ensure the steel strip of this invention has a long service life, and considering both impact toughness and weldability while also being economical, the Si content in this invention is controlled within the range of 0.96%-1.10%.

[0052] Practice has shown that manganese (Mn) can form a substitutional solid solution in steel, resulting in solid solution strengthening and a linear increase in strength. Mn is an austenite-forming element, stabilizing austenite, lowering the austenite transformation temperature (Ar3), increasing the ferrite nucleation rate, and reducing the grain growth rate, thus refining the grain size. However, increasing the Mn content increases the carbon equivalent (Ceq) of the steel, which is detrimental to weldability. To achieve high strength in the steel strip of this embodiment, and considering both weldability and economy, the Mn content is controlled within the range of 0.21%-0.30%.

[0053] 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 ensure the steel strip of this invention has a long service life, and considering strength, processing performance, and weldability while also being economical, the P content in this invention is controlled within the range of 0.041%-0.055%.

[0054] Practice 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 steel to form MnS plastic inclusions with S 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, which correspondingly reduces the transverse impact toughness and formability of the steel strip, and also leads to anisotropy in mechanical properties. 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 corrosion resistance, uniformity of mechanical properties, and processing performance of the steel strip in the embodiments of this invention, while also taking into account economy and production efficiency, the S content in the embodiments of this invention is controlled within the range of 0.0031%-0.0040%.

[0055] Practical experience has shown that Cu forms precipitates on the surface of steel, acting as a cathode to cause anodic passivation of the steel surface, and accumulates 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 can increase product costs. Considering the corrosion resistance, hot working performance, and surface quality of the 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%.

[0056] 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 plasticity and toughness of the steel, which will correspondingly worsen the formability and weldability, and increase the cost of the alloy. In order to achieve a long service life for the steel strip in the embodiments of the present invention, and taking into account plasticity, toughness, processing performance, weldability, and economy, the Cr content in the embodiments of the present invention is controlled within the range of 3.4%-3.6%.

[0057] Practice has shown that Al has great potential in improving the corrosion resistance of steel and reducing costs. Under marine atmospheric conditions, Al-Si alloyed steel has a synergistic effect in improving the corrosion resistance of steel. The generated FeAl2O4 fine-grained spinel oxide can enhance the barrier effect of the rust layer against corrosive media and moisture. The fine AlN formed by Al and N can inhibit the growth of austenite grains during the heating process of continuously cast billets, thus refining the grains and improving the strength, toughness, and weldability of steel. However, excessively high Al content leads to more Al2O3 inclusions, which on the one hand reduces the purity of the steel and the impact performance and surface quality of the steel strip, and on the other hand, makes it very easy for the nozzle to clump and clog during continuous casting, increasing production difficulty, reducing production efficiency, and increasing alloy and manufacturing costs. Considering the corrosion resistance, strength, toughness, weldability, machinability, impact performance, and surface quality of the long-life steel strip in the embodiments of the present invention, and taking into account production difficulty, production efficiency, and economy, the Alt content in the embodiments of the present invention is controlled within the range of 0.13%-0.16%.

[0058] In step S001, the continuously cast billet also needs to satisfy C / Cu≤1.2.

[0059] 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 / Cu ratio increases, the solubility of Cu in austenite decreases, the segregation of Cu at grain boundaries increases, and the tendency to generate network crack defects during hot rolling intensifies. Considering the strength, processing performance, and surface quality of the long-life steel strip in this embodiment of the invention, the C / Cu ratio is controlled to be ≤1.2.

[0060] In this embodiment of the invention, the selection of the contents of C, Si, Mn, P and Cr has a synergistic effect. By controlling the contents of each element within the above range, the effects of solid solution strengthening, grain refinement strengthening and phase transformation strengthening can be fully utilized, so that the long-life low-alloy corrosion-resistant steel for photovoltaic brackets has high strength and excellent cold working performance.

[0061] In this embodiment of the invention, the selection of the content of Si, P, S, Cu, Cr and Alt elements has a synergistic effect. By controlling the content 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 low alloy corrosion-resistant steel for photovoltaic brackets has a long service life and high corrosion resistance, which can meet the requirement of 25 years of service in C1-C4 environment, without the need for subsequent pickling, painting and maintenance, and is energy-saving and environmentally friendly.

[0062] In this embodiment of the invention, the content of C, Mn, S, Cu, and Alt elements and the selection of C / Cu have a synergistic effect. By controlling the content of each element and C / Cu within the above range, defects such as hot-rolled network cracks can be avoided, and the long-life low-alloy corrosion-resistant steel for photovoltaic brackets has excellent hot working performance and high surface quality, which can meet the stringent processing and service requirements of photovoltaic brackets.

[0063] In this embodiment of the invention, the selection of the content of all the above elements and the C / Cu ratio has a synergistic effect. By controlling the content of all elements and the C / Cu ratio within the above range, the long-life low-alloy corrosion-resistant steel for photovoltaic brackets is easy to process, has high production efficiency, low manufacturing cost, and short delivery cycle.

[0064] Specifically, step S001, obtaining the continuously cast billet through pretreatment, involves: desulfurizing the molten iron through pretreatment, smelting in a top-and-bottom combined blowing converter, refining in an LF refining furnace, and continuous casting of slabs to obtain the continuously cast billet.

[0065] 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.

[0066] The continuous casting billet has a tapping temperature of 1170-1190℃ and a cumulative furnace dwell time of 180-210 minutes.

[0067] Practice has shown that if the tapping temperature of the continuously cast billet is below 1170℃, the austenite grains can be refined, but the billet has poor thermoplasticity, high deformation resistance, and is difficult to hot-deform, thus leading to a low subsequent rolling mill operating rate. If the tapping temperature of the continuously cast billet is above 1190℃, although the thermoplasticity of the billet increases, the deformation resistance decreases, and it is easy to hot-deform, resulting in a higher subsequent rolling mill operating rate, the austenite grains tend to coarsen. Taking all these factors into consideration, the embodiment of this invention controls the tapping temperature of the continuously cast billet to 1170-1190℃.

[0068] 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 1120-1140℃ and the final rolling temperature to be 1050-1090℃, and using a roughing mill to roll the continuously cast billet to obtain a strip billet.

[0069] 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 increase, which is not conducive to the smooth progress of rolling. Taking all the above effects into consideration, the embodiment of this invention controls the rough rolling start temperature to 1120-1140℃ and the rough rolling finish temperature to 1050-1090℃.

[0070] The thickness of the strip obtained from rough rolling is 28-40 mm. The rough rolling process consists of 7 passes, with the following rolling speeds for each pass: Pass 1: 1.8-2.2 m / s, Pass 2: 2.4-2.8 m / s, Pass 3: 3.3-3.7 m / s, Pass 4: 3.8-4.2 m / s, Pass 5: 3.8-4.2 m / s, Pass 6: 4.8-5.2 m / s, and Pass 7: 5.3-5.7 m / s. Specific rolling speeds for each pass are shown in Table 1.

[0071] Table 1. Rolling speed in the roughing process of steel coils for photovoltaic brackets.

[0072]

[0073] Practice has shown that if the strip is too thick, the cumulative reduction rate and pass reduction rate of roughing rolling will decrease, making partial recrystallization more likely and causing mixed crystal phenomena. 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 the stability of finishing rolling. If the strip is too thin, it is not conducive to improving the strip shape quality and will increase the rolling load and energy consumption of the roughing mill, hindering smooth rolling. Furthermore, it cannot guarantee the finishing rolling start temperature required for rolling the 1.5-4.0mm thin-gauge finished steel strip of this invention, and may even increase the rolling load and energy consumption of the finishing mill. Considering all these factors, the embodiment of 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 reasonable number of rolling passes for the roughing mill can be calculated to be 7 passes.

[0074] If the rolling speed of each pass in the roughing mill is lower than the lower limit specified in Table 1, the rolling efficiency of the roughing mill will decrease, reducing output. If the rolling speed of each pass is higher than the upper limit specified in Table 1, the deformation resistance and rolling load of the roughing mill will increase. Taking all the above factors into consideration, the rolling speeds for the seven passes of the roughing mill are determined to be 1.8-2.2 m / s, 2.4-2.8 m / s, 3.3-3.7 m / s, 3.8-4.2 m / s, 3.8-4.2 m / s, 4.8-5.2 m / s, and 5.3-5.7 m / s, respectively.

[0075] Specifically, step S004 involves using a finishing mill to finish-roll the strip to obtain hot-rolled steel strip by controlling the initial rolling temperature of the finishing mill to be 990-1040℃ and the final rolling temperature of the finishing mill to be 840-880℃, and using a finishing mill to finish-roll the strip to obtain hot-rolled steel strip.

[0076] 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 factors into consideration, this embodiment of the invention controls the finishing rolling start temperature to be 990-1040℃.

[0077] 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 840-880℃.

[0078] The thickness of the hot-rolled steel strip obtained by finishing rolling is 1.5-4.0 mm. Finishing rolling is carried out using a 7-stand finishing mill. The rolling speeds of each stand are as follows: Stand 1: 0.96-1.26 m / s; Stand 2: 1.63-2.34 m / s; Stand 3: 2.5-3.82 m / s; Stand 4: 3.41-5.5 m / s; Stand 5: 4.26-7.37 m / s; Stand 6: 5.27-9.07 m / s; Stand 7: 6.22-10.37 m / s. The rolling speeds of each stand are shown in Table 2.

[0079] Table 2. Rolling speed of each stand in the finishing rolling process of a steel coil for a photovoltaic bracket.

[0080]

[0081] The choice between using a 7-stand finishing mill for finishing 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.

[0082] Practice has shown that if the rolling speed of each stand in the finishing mill is lower than the lower limit specified in Table 2, the rolling efficiency will decrease, reducing output; if the rolling speed is higher than the upper limit specified in Table 2, the deformation resistance and rolling load of each stand in the finishing mill will increase. Taking all the above factors into consideration, the rolling speeds of each stand in the finishing mill are determined to be 0.96-1.26 m / s, 1.63-2.34 m / s, 2.5-3.82 m / s, 3.41-5.5 m / s, 4.26-7.37 m / s, 5.27-9.07 m / s, and 6.22-10.37 m / s, respectively.

[0083] In step S005, the hot-rolled steel strip is cooled and then coiled into a steel coil. Specifically, the hot-rolled steel strip being transported on the laminar flow cooling roller conveyor is cooled, wherein the cooling method of the hot-rolled steel strip on the laminar flow cooling roller conveyor is post-cooling, and the flow rate ratio of the cooling water in the upper and lower manifolds is 8:12 during the cooling process; and the coiling temperature is controlled at 530-570℃, and the cooled hot-rolled steel strip is coiled into a steel coil using a coiling machine.

[0084] 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. It can reduce the solid solution carbon content in the ferrite grains and increase the density of movable dislocations, thereby achieving a good match between the strength, toughness, plasticity and cold forming performance of the finished steel strip.

[0085] 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, successfully coiling it and avoiding rolling accidents such as coiling and steel piling. Taking all the above factors into consideration, the cooling method for hot-rolled steel strip on the laminar flow cooling roller conveyor in this embodiment is post-cooling.

[0086] Practice has shown that if the cooling water flow ratio between the upper and lower manifolds is higher or lower than 8:12, 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 strip 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 8:12.

[0087] 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 530-570℃.

[0088] The preparation method further includes, after cooling the hot-rolled steel strip in step S005 and coiling the cooled hot-rolled steel strip into a steel coil:

[0089] Within 15 minutes, the steel coil unloaded from the coiler is hoisted into a slow cooling pit for slow cooling, with the temperature of the steel coil entering the slow cooling pit being ≥480℃; and the steel coil is hoisted out of the slow cooling pit after 60-66 hours of slow cooling.

[0090] 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 strip 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 rapidly places the coiled steel strip into a slow cooling pit for slow cooling. If the temperature of the coil entering the slow cooling pit is below 480°C and the slow cooling time is less than 60 hours, the effect of releasing internal stress and improving microstructure uniformity is poor. If the slow cooling time is longer than 66 hours, production efficiency will decrease. Controlling the time from uncoiling to loading into the slow cooling pit to within 15 minutes is a necessary measure to ensure that the temperature of the coil entering the slow cooling pit is ≥480°C. Considering all the above factors, this embodiment of the invention requires that the steel coil be hoisted into the slow cooling pit within 15 minutes after uncoiling from the coiler, with the temperature of the steel coil entering the slow cooling pit ≥480°C, and the steel coil be hoisted out of the slow cooling pit after slow cooling for 60-66 hours.

[0091] 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.

[0092] The preparation methods of Examples 1-3 of this invention include the following steps:

[0093] First, continuously cast billets are obtained through hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining, and slab continuous casting.

[0094] Table 3 shows a comparison of the chemical composition of the continuous casting billets obtained in Examples 1-3 of this invention with that of the continuous casting billets in Comparative Examples 1-3.

[0095] Table 3. Comparison of chemical composition (mass percentage) of continuous casting billets of Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0096]

[0097] Secondly, the continuously cast billet is heated, rough rolled, finish rolled, and cooled to obtain hot-rolled steel strip, which is then coiled and slowly cooled to obtain hot-rolled steel coil. The process parameters used in Examples 1-3 and Comparative Examples 1-3 of this invention are shown in Tables 4-5. The performance parameters of the steel coils of Examples 1-3 obtained from the chemical composition in Table 3 and the process parameters in Tables 4-5, as well as the performance parameters of the steel coils of Comparative Examples 1-3 obtained from the chemical composition in Table 3 and the process parameters in Tables 4-5, are shown in Table 6.

[0098] Table 4. Heating and roughing process parameters for Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0099]

[0100]

[0101] Table 5. Finishing and laminar flow cooling process parameters for Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0102]

[0103] Table 6 shows the slow cooling process parameters and steel coil properties of Examples 1-3 of the present invention, as well as the steel coil properties of Comparative Examples 1-3.

[0104]

[0105]

[0106] As can be seen from Tables 3-6, there are significant differences in chemical composition, heating, rough rolling, finish rolling, cooling, and other process parameters between Examples 1-3 and Comparative Examples 1-3 of the present invention, resulting in significant differences in the various properties of the obtained steel coils. The long-life low-alloy corrosion-resistant steel for photovoltaic brackets of the present invention can better meet the new requirements for photovoltaic bracket development, such as high strength, lightweight, high corrosion resistance, long life, easy manufacturing, low cost, high efficiency, paint-free, maintenance-free, energy saving, and environmental protection.

[0107] The preparation method of this invention optimizes the content of elements such as C, Si, Mn, P, S, Cu, Cr, and Alt, and controls the C / Cu ratio, continuous casting billet exit temperature, furnace dwell time, roughing rolling start and finish rolling temperatures, rolling passes, strip thickness, rolling speed, finishing rolling start and finish rolling temperatures, rolling passes, finished product thickness, rolling speed, cooling method, cooling water flow ratio of upper and lower manifolds, coiling temperature, and cooling method of the coiled steel. This ensures that the yield strength of the obtained steel is ≥690MPa, tensile strength is ≥800MPa, elongation after fracture is ≥18%, and it passes the 180°d=a cold bending test. After 72 hours of periodic immersion in a mixed solution of 0.01mol / L NaHSO3 and 3.5% NaCl, the corrosion rate is ≤1.8g / (m³). 2 •h); The uniform corrosion on one side of the steel coils prepared using the embodiments of the present invention after 25 years of uncoated service in C1, C2, C3 and C4 environments is ≤4μm, ≤12μm, ≤26μm and ≤45μm, respectively.

[0108] 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 33% compared to Q235B galvanized steel sheets, demonstrating significant weight reduction. They possess strong corrosion resistance, meeting the requirement of 25 years of paint-free service in C1-C4 environments, ensuring a long service life. Excellent formability meets the stringent processing requirements of photovoltaic brackets. Moderate P and Al content and low Cu content avoid adverse effects on plasticity, toughness, weldability, and surface quality, resulting in stable mechanical properties, low manufacturing difficulty, and high production efficiency. Free from expensive alloying elements such as W, Ni, Nb, V, and Mo, and with low Mn content, the alloy cost is lower. No subsequent pickling, painting, or maintenance is required, making it energy-saving, environmentally friendly, with short delivery cycles and low operating costs.

[0109] 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, low cost, high efficiency, no painting required, no maintenance required, energy saving, and environmental protection.

[0110] This invention also provides a steel coil for photovoltaic brackets, which is prepared by the preparation method of any of the above embodiments.

[0111] Among them, the yield strength of the steel coil is ≥690MPa, the tensile strength is ≥800MPa, the elongation after fracture is ≥18%, and the 180°d=a cold bending test is qualified.

[0112] The corrosion rate of steel coils after cyclic immersion in a mixed solution of 0.01 mol / L NaHSO3 and 3.5% NaCl for 72 hours is ≤1.8 g / (m²). 2 ·h).

[0113] The uniform corrosion on one side of the steel coil after 25 years of uncoated service in C1, C2, C3, and C4 environments is ≤4μm, ≤12μm, ≤26μm, and ≤45μm, respectively.

[0114] 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: 0.14%-0.16%, Si: 0.96%-1.10%, Mn: 0.21%-0.30%, P: 0.041%-0.055%, S: 0.0031%-0.0040%, Cu: 0.13%-0.18%, Cr: 3.4%-3.6%, Alt: 0.13%-0.16%, with the remainder being Fe and unavoidable impurities. Furthermore, the continuously cast billet must satisfy C / Cu ≤ 1.

2. The cooling process of the hot-rolled steel strip and the subsequent coiling of the cooled hot-rolled steel strip into a steel coil specifically involves: cooling the hot-rolled steel strip transported on the laminar flow cooling roller conveyor, wherein the cooling method of the hot-rolled steel strip on the laminar flow cooling roller conveyor is post-cooling, and the flow rate ratio of the upper and lower manifold cooling water during the cooling process is 8:12; and controlling the coiling temperature to 530-570℃, and using a coiling machine to coil the cooled hot-rolled steel strip into a steel coil. After cooling the hot-rolled steel strip and coiling the cooled hot-rolled steel strip into a steel coil, the method further includes: hoisting the steel coil unloaded from the coiler into a slow cooling pit for slow cooling within 15 minutes, wherein the temperature of the steel coil entering the slow cooling pit is ≥480℃; and hoisting the steel coil out of the slow cooling pit after slow cooling for 60-66 hours.

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 in an LF refining process, 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 continuous casting billet is subjected to heating and heat preservation treatment, wherein the billet's tapping temperature is 1170-1190℃ and the cumulative furnace dwell time is 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 1120-1140℃ and the final rolling temperature of the roughing mill to be 1050-1090℃, and using a roughing mill to roll the continuously cast billet to obtain a strip billet. The thickness of the strip obtained from rough rolling is 28-40 mm. The rough rolling process consists of 7 passes, with the following rolling speeds: Pass 1: 1.8-2.2 m / s, Pass 2: 2.4-2.8 m / s, Pass 3: 3.3-3.7 m / s, Pass 4: 3.8-4.2 m / s, Pass 5: 3.8-4.2 m / s, Pass 6: 4.8-5.2 m / s, and Pass 7: 5.3-5.7 m / s.

5. The preparation method according to claim 1, characterized in that, The process of using a finishing mill to finish rolling the strip billet to obtain hot-rolled steel strip specifically involves: controlling the initial rolling temperature of the finishing mill to be 990-1040℃ and the final rolling temperature of the finishing mill to be 840-880℃, and using a finishing mill to finish rolling the strip billet to obtain hot-rolled steel strip. The thickness of the hot-rolled steel strip obtained by finishing rolling is 1.5-4.0 mm. Finishing rolling is carried out using a 7-stand finishing mill. The rolling speed of each stand is as follows: 1st stand 0.96-1.26 m / s, 2nd stand 1.63-2.34 m / s, 3rd stand 2.5-3.82 m / s, 4th stand 3.41-5.5 m / s, 5th stand 4.26-7.37 m / s, 6th stand 5.27-9.07 m / s, and 7th stand 6.22-10.37 m / s.

6. A steel coil for a photovoltaic support structure, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

7. The steel coil according to claim 6, characterized in that, The steel coil has a yield strength ≥690MPa, tensile strength ≥800MPa, elongation after fracture ≥18%, and passes the 180°d=a cold bending test.

8. The steel coil according to claim 7, characterized in that, The corrosion rate of the steel coil after cyclic immersion in a mixed solution of 0.01 mol / L NaHSO3 and 3.5% NaCl for 72 hours was ≤1.8 g / (m³). 2 •h); The uniform corrosion on one side of the steel coil after 25 years of uncoated service in C1, C2, C3 and C4 environments is ≤4μm, ≤12μm, ≤26μm and ≤45μm, respectively.

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