Steel coil for photovoltaic support and method for manufacturing thereof

Abstract

The application relates to a steel coil for a photovoltaic support and a preparation method thereof, and the preparation method comprises the following steps: obtaining a continuous casting blank; rolling the continuous casting blank to obtain a hot-rolled steel strip; and coiling the steel strip into a steel coil; according to mass percentage, the continuous casting blank comprises the following components: C: 0.08%-0.10%, Si: 0.55%-0.64%, Mn: 0.51%-0.60%, P: 0.056%-0.065%, S: 0.0050%-0.0060%, Cu: 0.13%-0.18%, Cr: 2.8%-3.0%, Ti: 0.026%-0.035%, Alt: 0.17%-0.20%, and the rest is Fe and inevitable impurities. The steel coil prepared by the application can better meet the new requirements of the development of the photovoltaic support.

Description

Technical Field

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

[0002] Currently, the steel used for photovoltaic brackets is mainly plain carbon steel as the base material, and hot-dip galvanizing or zinc-aluminum-magnesium plating is used to improve corrosion resistance. However, hot-dip galvanizing or zinc-aluminum-magnesium plating will pollute the environment, increase production steps, extend the process flow, and increase manufacturing costs. Furthermore, the coating is easily damaged during transportation and processing, causing corrosion of the base material. Post-construction maintenance is necessary to prevent premature failure.

[0003] Photovoltaic brackets made of weathering steel exhibit significantly improved corrosion resistance during service due to the formation of a dense protective rust layer on their surface. Furthermore, this rust layer is self-healing after damage, eliminating the need for subsequent acid washing, painting, and maintenance. Therefore, using weathering steel to manufacture photovoltaic brackets offers advantages such as environmental friendliness, energy efficiency, high efficiency, and low cost. However, most existing weathering steels contain expensive alloying elements such as Ni and Nb, resulting in higher alloy costs, insufficient corrosion resistance, poor hole-expanding performance, and weak competitiveness, hindering large-scale application.

[0004] The prior art discloses a low-cost 650MPa grade titanium-containing weathering steel for photovoltaic brackets and its preparation method. The chemical composition of the titanium-containing weathering steel 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: 0.065%~0.105%, N: ≤0.0050%, with the remainder being Fe and unavoidable impurities. The thickness of the titanium-containing weathering steel is 1.5~4.0mm, the I index is 7.54-9.04, the tensile strength is 683-705MPa, and the elongation after fracture is 23.5-26%. However, the high phosphorus (P) content in the aforementioned photovoltaic (PV) bracket steel leads to severe segregation in the cast billet, reducing 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. Furthermore, the high content of the precious alloying element Cu in these PV bracket steels results in high product costs and a tendency to generate network crack defects during hot rolling. The high Ti content causes coarse TiN precipitates to easily become stress concentration points and microcrack initiations, consequently reducing the formability and fatigue performance of the PV bracket. The unstable Ti recovery rate leads to large fluctuations in mechanical properties, increasing the processing difficulty and reducing processing efficiency. Additionally, the aforementioned PV bracket steels lack data on hole expansion performance and formability, making material selection difficult for users.

[0005] Existing technology discloses a low-cost 650MPa grade antimony-containing weathering steel for photovoltaic brackets and its preparation method. The chemical composition of the antimony-containing weathering steel 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: 0.065%–0.105%, N: ≤0.0050%, Sb: 0.05%–0.07%, with the remainder being Fe and unavoidable impurities. The antimony-containing weathering steel has a thickness of 1.5–4.0 mm, an I-index of 7.67–9.04, a tensile strength of 680–700 MPa, and an elongation after fracture of 23.5%–26%. However, the high phosphorus (P) content in the aforementioned photovoltaic (PV) bracket steel leads to severe segregation in the cast billet, reducing 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 Cu results in high product costs and a tendency to generate network crack defects during hot rolling. The high Ti content causes coarse TiN precipitates to easily become stress concentration points and microcrack initiations, correspondingly reducing the formability and fatigue performance of the PV bracket. The unstable Ti recovery rate 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, tends to agglomerate at grain boundaries, weakens grain boundaries, and increases the tendency for intergranular brittle fracture, significantly reducing 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 hole expansion performance and formability, making material selection difficult for users.

[0006] Existing technology also discloses a 650MPa grade high weathering steel for photovoltaic brackets and its preparation method. The chemical composition of the high weathering steel includes: C: ≤0.08%, Si: 0.20%–0.30%, Mn: 0.40%–0.60%, P: ≤0.02%, S: ≤0.010%, Cu: 0.20%–0.40%, Cr: 2.50%–3.00%, Ni: 0.20%–0.30%, Nb: 0.005%–0.015%, Ti: 0.050%–0.090%, N: ≤0.0050%, with the remainder being Fe and unavoidable impurities. The high weathering steel has a thickness of 1.5mm–4.0mm, an I index of 8.11–9.59, a tensile strength of 675–705MPa, and an elongation after fracture of 24–26%. However, the aforementioned 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. Furthermore, the addition of precious alloying elements such as Ni and Nb further increases the alloy cost. The 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 the photovoltaic bracket. The unstable Ti recovery rate results in large fluctuations in mechanical properties, increasing the processing difficulty and reducing processing efficiency. Simultaneously, the aforementioned photovoltaic bracket steel lacks data on hole expansion performance and formability, making material selection difficult for users.

[0007] It can be seen that the steel used in photovoltaic brackets in the existing technology has a high content of precious metal elements, which increases the production cost. In addition, the overall performance of the steel is relatively poor, and there are also problems such as high production difficulty and low production efficiency, which need to be improved. Summary of the Invention

[0008] To address all or part of the aforementioned problems, the present invention aims to provide a steel coil for photovoltaic brackets and its preparation method. The preparation method of the present invention makes it easier to produce hot-rolled steel coils; the resulting steel coils have good hole expansion performance, high strength, and excellent corrosion resistance.

[0009] According to one aspect of the present invention, a method for manufacturing a steel coil for a photovoltaic support is provided, comprising:

[0010] Continuous casting billets are obtained through pretreatment;

[0011] The continuously cast billet is heated and held at a constant temperature.

[0012] The continuously cast billet is rough-rolled using a roughing mill to obtain a strip billet;

[0013] The strip is finished by a finishing mill to obtain hot-rolled steel strip; and

[0014] The hot-rolled steel strip is cooled and then coiled into a steel coil.

[0015] The continuously cast billet comprises the following components by mass percentage:

[0016] C: 0.08%-0.10%, Si: 0.55%-0.64%, Mn: 0.51%-0.60%, P: 0.056%-0.065%, S: 0.0050%-0.0060%, Cu: 0.13%-0.18%, Cr: 2.8%-3.0%, Ti: 0.026%-0.035%, Alt: 0.17%-0.20%, with the remainder being Fe and unavoidable impurities. Furthermore, the continuously cast billet must satisfy C+2P≤0.30%.

[0017] Furthermore, the process of obtaining the continuous casting billet through pretreatment specifically involves: desulfurizing the molten iron through pretreatment, smelting in a top-and-bottom combined blowing converter, refining in an LF refining process, and continuous casting of slabs to obtain the continuous casting billet; the thickness of the continuous casting billet is 180-230mm.

[0018] 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.

[0019] The continuous casting billet has a tapping temperature of 1190-1210℃ and a cumulative furnace dwell time of 180-210 minutes.

[0020] 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 1140-1160℃ and the final rolling temperature of the roughing mill to be 1070-1110℃, and using a roughing mill to roll the continuously cast billet to obtain a strip billet.

[0021] The thickness of the strip obtained by rough rolling is 28-40 mm, the number of rolling passes in rough rolling is 7, and the cumulative reduction rate of rough rolling is 82.6-87.8%.

[0022] 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 1010-1060℃ and the final rolling temperature of the finishing mill to be 860-900℃, and using a finishing mill to finish-roll the strip billet to obtain hot-rolled steel strip.

[0023] 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 unit, and the cumulative reduction rate of finishing rolling is 90-94.3%.

[0024] Furthermore, the cooling treatment of the hot-rolled steel strip and the winding 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; and controlling the winding temperature to 170-210℃, and using a coiler to wind the cooled hot-rolled steel strip into a steel coil.

[0025] Furthermore, the cooling treatment of the hot-rolled steel strip transported on the laminar flow cooling roller conveyor specifically includes:

[0026] The hot-rolled steel strip transported on the laminar flow cooling roller conveyor is subjected to the first stage of water cooling at a cooling rate of ≥110℃ / S to cool the steel strip to 660-690℃; after air cooling for 3-5S, the air-cooled steel strip is subjected to the second stage of water cooling at a cooling rate of ≥100℃ / S.

[0027] The present invention also provides a steel coil for photovoltaic brackets, which is prepared by any of the above-described preparation methods.

[0028] Furthermore, the microstructure of the steel coil is ferrite and martensite, wherein the proportion of ferrite is 70-90% and the proportion of martensite is 10-30%.

[0029] The steel coil has a yield strength ≥550MPa, tensile strength ≥650MPa, yield ratio ≤0.80, and elongation after fracture ≥25%.

[0030] After the steel coil was periodically immersed in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate relative to Q355B ordinary steel was ≤28%.

[0031] The straight seam welded steel pipe made from the steel coil showed no cracks in the base material during the 60° flaring test.

[0032] 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:

[0033] 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 hole expansion, high corrosion resistance, long life, easy manufacturing, low cost, high efficiency, no coating, no maintenance, energy saving, and environmental protection. Attached Figure Description

[0034] 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.

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0036] Figure 1 This is a flowchart of the preparation method according to an embodiment of the present invention;

[0037] Figure 2 A schematic diagram of the base material after the 60° flaring test of a straight seam welded steel pipe sample obtained using the steel coil of this embodiment of the 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: 0.08%-0.10%, Si: 0.55%-0.64%, Mn: 0.51%-0.60%, P: 0.056%-0.065%, S: 0.0050%-0.0060%, Cu: 0.13%-0.18%, Cr: 2.8%-3.0%, Ti: 0.026%-0.035%, Alt: 0.17%-0.20%, with the remainder being Fe and unavoidable impurities.

[0048] The steel coil prepared by the method of the present invention has a tensile strength of over 650 MPa and good hole expansion performance.

[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 adding carbon (C) to steel is an effective and economical way to improve its strength. Appropriate amounts of C combine with Ti to form TiC nanoscale precipitates, exhibiting significant grain refinement and precipitation strengthening effects. However, as the C content increases, the steel's plasticity, porosity, impact toughness, weldability, formability, and corrosion resistance decrease. To achieve a tensile strength of over 650 MPa in the steel strip of this invention, and considering processing performance, weldability, and corrosion resistance while also maintaining economic efficiency, the C content in this invention is controlled within the range of 0.08%-0.10%.

[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, effectively improving the strength of steel and its corrosion resistance. However, excessively high Si content reduces the material's toughness and is detrimental to improving weldability. To achieve a tensile strength of over 650 MPa for the steel strip in this embodiment of the invention, and considering processing performance, weldability, and corrosion resistance while also taking into account economic efficiency, the Si content in this embodiment is controlled within the range of 0.55%-0.64%.

[0052] Practice has shown that manganese (Mn) has a solid solution strengthening effect in steel, linearly increasing its 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, as the Mn content increases, the carbon equivalent of the steel increases, which is detrimental to weldability. To achieve a tensile strength of over 650 MPa in the steel strip of this invention, while comprehensively considering processing performance, weldability, and economic efficiency, the Mn content in this invention is controlled within the range of 0.51%-0.60%.

[0053] Practice has shown that phosphorus (P) has the second-highest solid solution strengthening effect in steel after carbon (C), and it can also 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 650 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 in this invention is controlled within the range of 0.056%-0.065%.

[0054] Practice has shown that high sulfur (S) content can lead to "hot brittleness" defects in steel. Adding manganese (Mn) to steel to form MnS plastic inclusions is an effective measure to mitigate the harmful effects of S. However, during rolling, MnS extending along the rolling direction easily forms banded structures, which reduce the transverse impact toughness and formability of the steel strip, while also causing anisotropy in mechanical properties. S is detrimental to the corrosion resistance of steel, 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-expansion steel strip in the embodiments of the present invention, while also taking into account economy and production efficiency, the S content in the embodiments of the present invention is controlled within the range of 0.0050%-0.0060%.

[0055] Practice has shown that Cu can form a dense amorphous oxide protective layer on the surface of steel, thereby effectively improving the corrosion resistance of the 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 will increase product costs. Considering the hot working performance, surface quality, and corrosion resistance of the high-expansion steel strip in the embodiments of the present invention, while also taking into account economic efficiency, the Cu content in the embodiments of the present 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 ductility 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 tensile strength of over 650 MPa for the steel strip in the embodiments of the present invention, and taking into account corrosion resistance, ductility and toughness, processing performance, weldability, and economic efficiency, the Cr content in the embodiments of the present invention is controlled within the range of 2.8%-3.0%.

[0057] Practice has shown that TiN, formed by Ti and N, can inhibit austenite grain growth during the heating process of continuously cast billets, which is beneficial to improving the strength, toughness, and weldability of steel. Ti and C form nanoscale TiC precipitates during hot rolling, which have fine-grain strengthening and precipitation strengthening effects, improving the strength and toughness of steel. However, if the Ti content is high, on the one hand, coarse TiN precipitates are easily formed, becoming stress concentration points and microcrack initiations, reducing the forming and fatigue performance of photovoltaic brackets; on the other hand, the recovery rate of Ti is unstable, resulting in large fluctuations in mechanical properties. Therefore, excessively high Ti content will increase the processing difficulty of photovoltaic brackets and reduce processing efficiency. Considering the strength, toughness, weldability, processing performance, and service performance of the high-expansion steel strip in this embodiment of the invention, the Ti content is controlled within the range of 0.026%-0.035%.

[0058] Practice has shown that the fine AlN formed by Al and N can inhibit austenite grain growth during the heating process of continuously cast billets, thus refining the grains and improving the strength, toughness, and weldability of steel. In marine atmospheric environments, Al and Si work synergistically to create a rust layer that effectively blocks corrosive media and moisture. However, excessively high Al content leads to the formation of more Al2O3 inclusions, which reduces the purity of the steel, its impact resistance, corrosion resistance, and surface quality. Furthermore, it easily clogs the nozzle during continuous casting, increasing production difficulty, reducing production efficiency, and raising alloy and manufacturing costs. Considering the strength, weldability, machinability, corrosion resistance, and surface quality of the high-expansion steel strip in this embodiment of the invention, while also taking into account production difficulty, efficiency, and economy, the Alt content in this embodiment is controlled within the range of 0.17%-0.20%.

[0059] In step S001, the continuously cast billet must also satisfy C+2P≤0.30%.

[0060] Practical experience has shown that phosphorus (P) is a readily segregating element in steel, and its hardenability in the segregation region is approximately twice that of carbon (C). If C + 2P > 0.30%, the strength and hardness of the steel increase linearly with increasing C + 2P, while its ductility, toughness, and hole-expanding properties decrease. If C + 2P ≤ 0.30%, the influence of C + 2P on the mechanical properties and hole-expanding properties of the steel becomes less pronounced. Therefore, considering the comprehensive mechanical properties of the high-expanding steel strip in this embodiment of the invention, C + 2P is controlled to be ≤ 0.30%.

[0061] The selection of the contents of C, Si, Mn, P, S, Cu, Cr, Ti, and Alt elements and C+2P has a synergistic effect. By controlling the contents of each element and C+2P within the above range, the effects of solid solution strengthening, grain refinement strengthening, and phase transformation strengthening can be fully utilized, giving low-alloy corrosion-resistant steel for photovoltaic brackets high porosity, high purity, high strength, and excellent cold working performance.

[0062] The selection of the contents of the above-mentioned elements Si, P, S, Cu, Cr and Alt has a synergistic effect. By controlling the contents of each element within the above range, a dense internal rust layer can be formed on the surface of the steel matrix, so that the high-hole-expansion low-alloy corrosion-resistant steel for photovoltaic brackets has high corrosion resistance, can meet the service requirements, and does not require subsequent pickling, painting and maintenance, which is energy-saving and environmentally friendly.

[0063] The selection of C, Mn, S, Cu, and Alt 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, giving the high-hole-expansion low-alloy corrosion-resistant steel for photovoltaic brackets excellent hot working performance and high surface quality, which can meet the stringent processing and service requirements of photovoltaic brackets.

[0064] The content of all the above elements and the selection of C+2P have a synergistic effect. By controlling the content of all elements and C+2P within the above range, the high-hole-expansion low-alloy corrosion-resistant steel for photovoltaic brackets is easier to process, has higher production efficiency, lower manufacturing cost, and shorter delivery cycle.

[0065] Specifically, step S001, obtaining the continuous casting billet through pretreatment, involves: desulfurizing the molten iron through pretreatment, smelting in a top-and-bottom combined blowing converter, refining in an LF refining process, and continuous casting of slabs to obtain the continuous casting billet; the thickness of the continuous casting billet is 180-230mm.

[0066] Practice has shown that, given a fixed width and length of the continuously cast billet, a thicker billet results in higher output and yield, but also a greater mill load and greater fluctuations in the final rolling temperature, microstructure, and mechanical properties of the finished steel strip along its length. Furthermore, the billet thickness is limited by the maximum allowable outer diameter of the coil. Taking all these factors into account, this embodiment of the invention controls the continuously cast billet thickness to be 180-230 mm.

[0067] 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 in the walking beam furnace; the billet exiting the furnace at a temperature of 1190-1210℃, and the cumulative furnace dwell time of the billet being held in the furnace at a temperature of 180-210 minutes.

[0068] Practice has shown that if the tapping temperature of the continuously cast billet is below 1190℃, 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 1210℃, 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 1190-1210℃.

[0069] If the cumulative furnace dwell time of the continuously cast billet is less than 180 minutes, its microstructure is not easily homogenized, rolling energy consumption is high, and equipment accidents are prone to occur. If the cumulative furnace dwell time of the continuously cast billet is longer than 210 minutes, it is prone to oxidation and decarburization, which will increase energy consumption and reduce the rolling mill's operating rate and production efficiency. Taking all the above factors into consideration, the embodiment of the present invention controls the cumulative furnace dwell time of the continuously cast billet to 180-210 minutes.

[0070] 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 1140-1160℃ and the final rolling temperature of the roughing mill to be 1070-1110℃, and using a roughing mill to roll the continuously cast billet to obtain a strip billet.

[0071] Practice has shown that the main metallurgical purpose of rough rolling is to disrupt the as-cast structure of the continuously cast billet, effectively refine the austenite grains through multiple recrystallizations, and obtain a uniform and fine austenite structure. If the rough rolling start temperature is too high, austenite grain inhomogeneity will occur, leading to differences in the strip structure and affecting the uniformity of the finished product's mechanical properties. If the rough rolling start temperature is too low, the difficulty of controlling the strip shape increases, the mill load and rolling energy consumption rise, which is not conducive to smooth rolling. Taking all these factors into consideration, the embodiments of this invention control the rough rolling start temperature at 1140-1160℃ and the rough rolling finish temperature at 1070-1110℃.

[0072] The thickness of the strip obtained by rough rolling is 28-40 mm, the number of rolling passes in rough rolling is 7, and the cumulative reduction rate of rough rolling is 82.6-87.8%.

[0073] Practice has shown that if the strip is too thick and the cumulative reduction rate in roughing is too small, partial recrystallization is likely to occur, leading to mixed crystal formation. This negatively impacts the uniformity of the mechanical properties of the finished steel strip and increases the rolling load and energy consumption of the finishing mill, affecting finishing stability. Conversely, if the strip is too thin and the cumulative reduction rate in roughing is too large, it hinders the improvement of strip shape quality and increases the rolling load and energy consumption of the roughing mill, making rolling difficult and preventing the guarantee of the finishing mill's required starting temperature for rolling the 1.5-4.0mm thin-gauge finished steel strip of this invention. It may even increase the rolling load and energy consumption of the finishing mill. Considering all these factors, the embodiment of this invention controls the strip thickness to be 28-40mm and the cumulative reduction rate in roughing to be 82.6-87.8%. Based on the roughing mill's energy parameters, the thickness of the continuously cast billet and the strip, the optimal number of rolling passes for the roughing mill can be calculated to be 7 passes.

[0074] Specifically, step S004 involves using a finishing mill to finish-roll the strip to obtain hot-rolled steel strip. This involves controlling the initial rolling temperature of the finishing mill to be 1010-1060℃ and the final rolling temperature to be 860-900℃, and then using a finishing mill to finish-roll the strip to obtain hot-rolled steel strip.

[0075] Practice has shown that if the finishing rolling start temperature is too high, partial recrystallization can easily occur in the first stand (F1) and the second stand (F2), leading to mixed crystallization problems and abnormal fluctuations in the microstructure and mechanical properties of the finished steel strip. If the finishing rolling start temperature is too low, the desired final rolling temperature cannot be guaranteed. Taking all the above factors into consideration, the finishing rolling start temperature in this embodiment of the invention is controlled at 1010-1060℃.

[0076] 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 860-900℃.

[0077] 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 unit, and the cumulative reduction rate of finishing rolling is 90-94.3%.

[0078] Practice has shown that if the cumulative reduction rate in finishing rolling is too small, grain inhomogeneity will occur, which will correspondingly reduce the plasticity of the finished steel strip. If the cumulative reduction rate in finishing rolling is too large, the deformation resistance and load of each stand in the finishing mill will increase, leading to potential equipment hazards. Taking all the above factors into consideration, the cumulative reduction rate in finishing rolling is determined to be 90-94.3%.

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

[0080] Specifically, step S005 involves cooling the hot-rolled steel strip and coiling the cooled hot-rolled steel strip into a steel coil. This includes cooling the hot-rolled steel strip being transported on the laminar flow cooling roller conveyor and controlling the coiling temperature to 170-210℃, and using a coiler to coil the cooled hot-rolled steel strip into a steel coil.

[0081] Specifically, the cooling treatment of the hot-rolled steel strip transported on the laminar flow cooling roller conveyor includes:

[0082] The hot-rolled steel strip transported on the laminar flow cooling roller conveyor is subjected to the first stage of water cooling at a cooling rate of ≥110℃ / S to cool the steel strip to 660-690℃; after air cooling for 3-5S, the air-cooled steel strip is subjected to the second stage of water cooling at a cooling rate of ≥100℃ / S.

[0083] Practice has shown that, given a fixed length of laminar flow cooling rollers, if the first-stage cooling rate is too low, subsequent cooling processes cannot be executed, and the desired microstructure and properties cannot be obtained. Therefore, the first-stage cooling rate should be increased as much as possible. Both excessively high and low first-stage water cooling termination temperatures cannot guarantee the formation of sufficient ferrite in the steel strip microstructure. Both excessively long and short air cooling times will not yield a microstructure with a suitable ferrite to martensite ratio. If the second-stage cooling rate is too low, martensite may not form in the steel strip microstructure; therefore, the second-stage cooling rate should be increased as much as possible. If the steel strip coiling temperature is above 210℃, supercooled austenite cannot transform into martensite; if the coiling temperature is below 170℃, controlling the steel strip shape and coil shape becomes more difficult. Taking all the above factors into consideration, the following is determined in this embodiment of the invention: the first stage cooling rate of the hot-rolled steel strip on the laminar flow cooling roller table is ≥110℃ / S, the temperature after the first stage water cooling is 660-690℃, the air cooling time is 3-5S, the second stage cooling rate is ≥100℃ / S, and the coiling temperature is 170-210℃.

[0084] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments. Experimental methods in the following embodiments, unless otherwise specified, are performed according to conventional methods and conditions.

[0085] The preparation methods of Examples 1-3 of this invention include the following steps:

[0086] First, continuously cast billets are obtained through hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining, and slab continuous casting.

[0087] Table 1 shows a comparison of the chemical composition of the continuous casting billets obtained in Examples 1-3 of the present invention with that of the continuous casting billets in Comparative Examples 1-3.

[0088] Table 1. Chemical composition (mass percentage) of continuous casting billets in Examples 1-3 of the present invention and comparative examples 1-3.

[0089]

[0090] Secondly, the continuously cast billet is heated, rough rolled, finish rolled, and cooled to obtain hot-rolled steel strip, which is then coiled to obtain hot-rolled steel coil. The process parameters used in Examples 1-3 and Comparative Examples 1-3 of this invention are shown in Tables 2-3. The performance parameters of the steel coils of Examples 1-3 obtained from the chemical composition in Table 1 and the process parameters in Tables 2-3, as well as the performance parameters of the steel coils of Comparative Examples 1-3 obtained from the chemical composition in Table 1 and the process parameters in Tables 2-3, are shown in Table 4.

[0091] Table 2 shows the heating and roughing process parameters for Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0092]

[0093] Table 3 shows the finishing, cooling, and coiling process parameters for Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0094]

[0095] Table 4 Performance of Examples 1-3 and Comparative Examples 1-3 of the present invention

[0096]

[0097] As can be seen from Tables 1-4, there are significant differences in chemical composition, heating, rough rolling, finish rolling, cooling, coiling, and other process parameters between Examples 1-3 and Comparative Examples 1-3 of the present invention, resulting in significant differences in the microstructure and various properties of the obtained steel coils. The steel coils prepared through the embodiments of the present invention can better meet the new requirements for photovoltaic bracket development, such as high strength, lightweight, high hole expansion, high corrosion resistance, long life, easy manufacturing, low cost, high efficiency, no coating required, maintenance-free, energy saving, and environmental protection.

[0098] The preparation method of this invention optimizes the content of elements such as C, Si, Mn, P, S, Cu, Cr, Ti, and Alt, and controls C+2P, the continuous casting billet exit temperature and holding time, the roughing rolling start and finish rolling temperatures, rolling passes, strip thickness, cumulative reduction rate, the finishing rolling start and finish rolling temperatures, rolling passes, finished product thickness, cumulative reduction rate, cooling method, and coiling temperature, so that the microstructure of the obtained finished steel consists of 70-90% ferrite and 1% Fe. The steel has a martensite content of 0-30%, and the resulting finished steel has a yield strength ≥550MPa, tensile strength ≥650MPa, yield ratio ≤0.80, and elongation after fracture ≥25%. After cyclic immersion in a 0.01mol / L NaHSO3 solution for 72 hours, the corrosion rate relative to Q355B ordinary steel is ≤28%. Straight seam welded steel pipes processed from steel coils using the steel coils of this embodiment show no cracks in the base material during a 60° flaring test. Figure 2 As shown.

[0099] The photovoltaic mounting brackets of this invention use high-expansion, low-alloy corrosion-resistant steel coils. These coils are free of sulfur (Sb) and have low levels of other harmful and impurity elements, resulting in pure steel. They possess high strength, reducing weight by 26% compared to Q235B galvanized steel sheets, demonstrating significant lightweighting. They exhibit strong corrosion resistance, meeting the service requirements of photovoltaic mounting brackets. Excellent formability meets the stringent processing requirements of photovoltaic mounting brackets. A low yield strength ratio minimizes springback during the manufacture of photovoltaic bracket components, facilitating easy forming. The large plasticity reserve of the photovoltaic brackets provides good shock resistance and impact resistance, with a large safety margin. Moderate P and Al content, and low Cu and Ti content, avoid their adverse effects on plasticity, weldability, and surface quality. Stable mechanical properties, low manufacturing difficulty, and high production efficiency are achieved. Free of precious alloying elements such as Ni, Nb, V, and Mo, and with low Mn content, the alloy cost is relatively low. No subsequent pickling, painting, or maintenance is required, resulting in energy saving, environmental friendliness, short delivery cycles, and low operating costs.

[0100] The high-perforation low-alloy corrosion-resistant steel coils for photovoltaic brackets in this invention embodiment can better meet the new requirements for the development of photovoltaic brackets, such as high strength, lightweight, high perforation, high corrosion resistance, long life, easy manufacturing, low cost, high efficiency, no painting required, no maintenance, energy saving, and environmental protection.

[0101] This invention also provides a steel coil for photovoltaic brackets, which is prepared by the preparation method of any of the above embodiments.

[0102] The microstructure of the steel coil consists of ferrite and martensite, with ferrite accounting for 70-90% and martensite accounting for 10-30%.

[0103] The steel coil has a yield strength ≥ 550 MPa, tensile strength ≥ 650 MPa, yield ratio ≤ 0.80, elongation after fracture ≥ 25%, and passes the 180°d=a cold bending test;

[0104] After the steel coil was periodically immersed in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate was ≤28% compared to ordinary Q355B steel.

[0105] The straight seam welded steel pipe sample processed from the steel coil according to the embodiments of the present invention showed no cracks in the base material during the 60° flaring test, such as... Figure 2 As shown.

[0106] 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: 0.08%-0.10%, Si: 0.55%-0.64%, Mn: 0.51%-0.60%, P: 0.056%-0.065%, S: 0.0050%-0.0060%, Cu: 0.13%-0.18%, Cr: 2.8%-3.0%, Ti: 0.026%-0.035%, Alt: 0.17%-0.20%, with the remainder being Fe and unavoidable impurities. Furthermore, the continuously cast billet must satisfy C+2P≤0.30%. The cooling process specifically involves: first-stage water cooling of the hot-rolled steel strip transported on the laminar flow cooling roller conveyor at a cooling rate of ≥110℃ / S to cool the steel strip to 660-690℃; after air cooling for 3-5S, second-stage water cooling of the air-cooled steel strip at a cooling rate of ≥100℃ / S. The microstructure of the steel coil consists of ferrite and martensite, with ferrite accounting for 70-90% and martensite accounting for 10-30%.

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 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; wherein the furnace exit temperature of the continuous casting billet is 1190-1210℃, and the cumulative furnace dwell time of the continuous casting billet 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 1140-1160℃ and the final rolling temperature of the roughing mill to be 1070-1110℃, and using a roughing mill to roll the continuously cast billet to obtain a strip billet. The thickness of the strip obtained by rough rolling is 28-40 mm, the number of rolling passes in rough rolling is 7, and the cumulative reduction rate of rough rolling is 82.6-87.8%.

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 finishing rolling to be 1010-1060℃ and the final rolling temperature of finishing rolling to be 860-900℃, 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. The finishing rolling adopts a 7-stand finishing mill unit, and the cumulative reduction rate of finishing rolling is 90-94.3%.

6. The preparation method according to claim 1, characterized in that, The cooling treatment of the hot-rolled steel strip and the winding of the cooled hot-rolled steel strip into a steel coil specifically involves: cooling the hot-rolled steel strip being transported on a laminar flow cooling roller conveyor; and controlling the winding temperature to 170-210℃, and using a winding machine to wind the cooled hot-rolled steel strip into a steel coil.

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

8. The steel coil according to claim 7, characterized in that, After the steel coil was periodically immersed in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate relative to Q355B ordinary steel was ≤28%. The straight seam welded steel pipe made from the steel coil showed no cracks in the base material during the 60° flaring test.

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