CN116219307A - Low-cost 650 MPa-grade titanium-containing weathering steel for photovoltaic brackets and preparation method thereof - Google Patents

Abstract

The invention provides titanium-containing weathering steel for a low-cost 650 MPa-level photovoltaic bracket and a preparation method thereof. The invention comprises the following chemical components in percentage by weight: c: less than or equal to 0.08 percent, si:0.35 to 0.50 percent, mn:0.40 to 0.60 percent, P:0.08 to 0.12 percent, S: less than or equal to 0.010 percent, cu:0.25 to 0.40 percent, cr:0.75% -1.00%, ti:0.065% -0.105%, N: less than or equal to 0.0050 percent, and the balance of Fe and unavoidable impurities. The tensile strength of the hot rolled steel coil prepared by the method is more than or equal to 650MPa, and the weather resistance index I is more than or equal to 7.5. The forming performance and welding performance are good, the strength is high, the cost is low, the corrosion resistance is excellent, the service life of the photovoltaic bracket can be obviously prolonged when the photovoltaic bracket is applied to the photovoltaic bracket, and the cost and the labor intensity of the photovoltaic bracket are reduced.

Description

Low-cost 650 MPa-grade titanium-containing weathering steel for photovoltaic brackets and preparation method thereof

Technical Field

The invention relates to the technical field of metal materials, in particular to titanium-containing weather-resistant steel for a low-cost 650 MPa-level photovoltaic bracket and a preparation method thereof.

Background

The photovoltaic power generation is an environment-friendly industry, shows no comparably wide development space and application prospect by the characteristics of no pollution, no noise, simple maintenance and the like, and is the most potential energy development field. The photovoltaic support is an important supporting and protecting structure of the photovoltaic power generation device. In order to prevent corrosion of the photovoltaic bracket, steel plate coils made of Q235 and Q355 materials or galvanized steel plates after light profile processing are mostly adopted at present. But the hot dip galvanized product can cause pollution during production, thereby greatly increasing the treatment cost.

The high-strength weathering steel is an ideal product of the photovoltaic bracket, and the high-content noble alloy elements such as V, nb, ni and the like are added in the production of the photovoltaic bracket at home at present so as to achieve the purposes of improving the strength and corrosion resistance, but the production cost is increased, the strength is not high enough, and the corrosion resistance is not good enough. Therefore, the development of the weather-resistant steel for the 650 MPa-grade photovoltaic bracket with low cost, high strength and high corrosion resistance has very important significance.

Compared with the related patent document, CN113528949A discloses a hot rolled steel coil for a 550 MPa-level solar bracket and a production method thereof: the strength is improved by adopting Nb-V microalloying, the strength level is lower, the steel plate is thicker (the half size is more than or equal to 5mm and the half size is more than or equal to 10 mm) according to the low-temperature impact performance test requirement, the cost of the produced photovoltaic bracket is high, and the construction labor intensity is high.

CN114438411a discloses a weather resistant steel for a photovoltaic bracket and a production method thereof: the Nb-Ti microalloying is adopted to improve the strength, the strength grade is lower, and the tensile strength is lower: 420-600 MPa, the requirement of low-temperature impact performance test shows that the steel plate is thicker (more than or equal to 5mm is half-sized, more than or equal to 10mm is half-sized), the produced photovoltaic bracket has high cost, high construction labor intensity, poor corrosion resistance, weather resistance index of 6.37-6.60, high Ni content (0.015%) of precious metal in the embodiment, extremely low S content (0.001% and 0.002%), and high smelting and S removing cost.

CN113652599a discloses a high-strength corrosion-resistant cold-resistant hot rolled steel coil, a production method and application thereof: the V-Ti microalloying is adopted to improve the strength, the strength grade is lower, and the tensile strength in the embodiment is as follows: 425-480 MPa; the steel plate is thicker (3 mm-16 mm), the cost of the produced photovoltaic bracket is high, and the construction labor intensity is high; c:0.15 to 0.20 percent of the alloy has high content and poor welding performance; mn is 0.025 percent to 0.055 percent, the content is too low, the Mn-S ratio is too low, and edge cracks can be generated in industrial production; the corrosion resistance is very poor, and the weather-resistant element only contains 0.10 to 0.20 percent of Cu and 0.30 to 0.60 percent of Cr, so that the life cycle of the photovoltaic bracket for bare use for 25 to 30 years can not be satisfied.

Disclosure of Invention

According to the technical problems, the invention provides the weather-resistant steel for the low-cost 650 MPa-level photovoltaic bracket and the preparation method thereof, wherein Ti alloying is adopted, noble metals such as niobium, vanadium, nickel and the like are not added, the alloy cost is low, the strength is improved by controlling nano-grade precipitation, the thickness of the steel for the photovoltaic bracket is only 1.5mm-4.0mm, the weight is reduced by more than 25%, and meanwhile, the transportation cost and the construction labor intensity are reduced; by adding certain cheap and good silicon and phosphorus, the weather resistance index can be improved, the strength can be improved, the corrosion resistance is excellent, and the coating can be used bare; the components are reasonable in design, low in production cost and low in production difficulty, and the industrial production is facilitated. The invention adopts the following technical means:

the titanium-containing weathering steel for the low-cost 650 MPa-level photovoltaic bracket comprises the following chemical components in percentage by weight: c: less than or equal to 0.08 percent, si:0.35 to 0.50 percent, mn:0.40 to 0.60 percent, P:0.08 to 0.12 percent, S: less than or equal to 0.010 percent, cu:0.25 to 0.40 percent, cr:0.75% -1.00%, ti:0.065% -0.105%, N: less than or equal to 0.0050 percent, and the balance of Fe and unavoidable impurities.

In order to achieve the aim of the invention, the invention also discloses a technical scheme, namely a production method of the titanium-containing weathering steel for the low-cost 650 MPa-level photovoltaic bracket, which has the production steps basically the same as those of the existing hot-rolled strip steel production steps, and comprises the steps of hot rolling, cooling and coiling:

heating time in the hot rolling step is 60-100 min; the thickness of a finish rolling inlet in the hot rolling step is 30-40 mm, the initial rolling temperature of finish rolling is 980-1080 ℃, and the final rolling temperature in the hot rolling step is 880-920 ℃; in the cooling step, the laminar cooling is front-stage cooling; the temperature in the coiling step is 600-660 ℃, and the thickness is 1.5-4.0 mm.

The design reasons of the selection principle and the content of each chemical component and the main working procedures are as follows:

carbon: carbon is an effective strengthening element in steel, can be dissolved into a matrix to play a role in solid solution strengthening, and can be combined with titanium to form carbide precipitation particles to play a role in fine grain strengthening and precipitation strengthening, so that the improvement of the carbon content is beneficial to the improvement of strength. However, too high carbon content can form more coarse and brittle carbide particles in the steel, is unfavorable for plasticity and toughness, can easily form segregation bands in the center of the steel plate, is unfavorable for bending performance, forming performance and the like, and can increase welding carbon equivalent and welding crack sensitivity index, thereby being unfavorable for welding processing; therefore, the value range of C in the invention is set to be less than or equal to 0.08 percent.

Silicon: silicon can be dissolved in ferrite and austenite to improve the hardness and strength of steel, which is favorable for refining rust layer structure and reducing the overall corrosion rate of steel, but too high content can reduce the plasticity and toughness of steel, so that the phosphorus is difficult to remove during rolling, and the welding performance can be reduced; therefore, the value range of Si in the invention is set to be 0.35-0.50%.

Manganese: manganese has a strong solid solution strengthening effect, can obviously reduce the phase transition temperature of steel, refines the microstructure of the steel, is an important strengthening element, but when the Mn content is excessive, the continuous casting process is easy to generate casting blank cracks, and meanwhile, the core component segregation of the steel plate can be caused, and the welding performance of the steel can be reduced; therefore, the range of Mn in the invention is set to be 0.40-0.60%.

Phosphorus: the phosphorus element can effectively improve the atmospheric corrosion resistance of the steel, but the too high phosphorus content can obviously reduce the plasticity and low-temperature toughness of the steel; therefore, the value range of P in the invention is set as P:0.08 to 0.12 percent.

Sulfur: sulfur can form sulfide inclusions to deteriorate the performance of steel, and hole corrosion expansion is easy to form in the corrosion process, so that the corrosion performance is adversely affected; therefore, the value range of S in the invention is set to be less than or equal to 0.010 percent.

Copper: copper is added into the steel, so that a compact amorphous oxide (hydrocarbyloxy) protective layer with good adhesiveness is formed on the surface of the steel, and the corrosion resistance is obvious; in addition, copper and sulfur generate insoluble sulfides, thereby counteracting the harmful effect of S on the corrosion resistance of the steel; however, when the copper content is too high, the melting point of copper is lower than the heating temperature of the steel billet, precipitated copper is gathered at an austenite grain boundary in a liquid state, and when the content of the precipitated copper reaches a certain degree, cracks are easily generated during heating or hot rolling; in addition, according to the calculation formula of the atmospheric corrosion resistance index I, the calculated value of I is reduced when the copper content is too small or too large; therefore, the value range of Cu in the invention is set to be 0.25-0.40%.

Chromium: chromium has remarkable effect of improving the passivation capability of steel, can promote the surface of the steel to carry out compact passivation film or protective rust layer, and the enrichment of the chromium in the rust layer can effectively improve the selective permeability characteristic of the rust layer to corrosive media; however, too high a chromium content increases the production cost; therefore, the value range of Cr in the invention is set to be 0.75-1.00%.

Titanium, nitrogen: ti (C, N) precipitates formed by titanium, carbon and nitrogen can effectively refine austenite grains and inhibit coarsening of a coarse grain region in the welding process, and can generate a precipitation strengthening effect: increasing the Ti element content can increase the volume fraction of Ti (C, N) precipitate and enhance the fine-grain strengthening and precipitation strengthening effects, but too high titanium or nitrogen element content is easy to form micron-sized TiN, so that the formability and fatigue performance are reduced, and too high nitrogen content can increase the ageing tendency, cold brittleness and hot brittleness of the steel, and the welding performance and cold bending performance of the steel are damaged; therefore, the value range of Ti is set to be 0.065% -0.105% and the value range of N is set to be less than or equal to 0.0050%.

The heating time in the hot rolling step is 60-100 min, the time is too short, and the dissolution of Ti is insufficient. The copper brittleness is easy to generate when the time is too long, and the quality of the steel hemming part is affected.

In the hot rolling step, the initial rolling temperature of finish rolling is 980-1080 ℃, the temperature is too low, the rolling rhythm is too slow, and the production efficiency is low. The temperature is too high, and the secondary oxide scale in the rolling process is thicker, which is unfavorable for the surface quality and the rolling stability.

The final rolling temperature in the hot rolling step is 880-920 ℃, the temperature is too low, the rolling speed is too low, and the rolling rhythm and the yield are affected. The temperature is too high, the cooling speed is too high, the structure is uneven, and the plasticity of the steel plate is affected.

The laminar cooling in the cooling step is front-stage cooling, which is favorable for inhibiting the growth of crystal grains and obtaining an ideal ferrite structure.

The temperature in the coiling step is 600-660 ℃, the temperature is too low, the precipitation strengthening effect of Ti is weakened, and the tensile strength is not high. The temperature is too high, the crystal grains of the finished product are coarse, and the toughness of the steel plate is poor. The cooling speed after finish rolling is improved by a front-stage cooling mode of laminar cooling, and the supersaturation precipitation of Ti element in ferrite in the coiling stage is enhanced by combining the coiling temperature of 600-660 ℃ suitable for Ti element precipitation, so that nano-grade precipitation is formed, and the precipitation strengthening effect is improved.

The tensile strength of the hot rolled steel coil prepared by the method is more than or equal to 650MPa, and the weather resistance index I is more than or equal to 7.5.

The hot rolled steel coil prepared by the method has good forming performance and welding performance, high strength, low cost and excellent corrosion resistance, and can obviously prolong the service life of the photovoltaic bracket and reduce the cost and labor intensity of the photovoltaic bracket when being applied to the photovoltaic bracket.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

The invention provides low-cost 650 MPa-level titanium-containing weathering steel for a photovoltaic bracket, which comprises the following chemical components in percentage by weight: c: less than or equal to 0.08 percent, si:0.35 to 0.50 percent, mn:0.40 to 0.60 percent, P:0.08 to 0.12 percent, S: less than or equal to 0.010 percent, cu:0.25 to 0.40 percent, cr:0.75% -1.00%, ti:0.065% -0.105%, N: less than or equal to 0.0050 percent, and the balance of Fe and unavoidable impurities.

The production method of the titanium-containing weathering steel for the low-cost 650 MPa-level photovoltaic bracket has the production steps basically the same as those of the existing hot rolled strip steel, and comprises the steps of hot rolling, cooling and coiling:

in the hot rolling step: heating time in the hot rolling step is 60-100 min; the thickness of the finish rolling inlet is 30 mm-40 mm, and the initial rolling temperature of finish rolling is 980-1080 ℃. The finishing temperature is 880-920 ℃. Laminar cooling is front-end cooling. The coiling temperature is 600-660 ℃ and the thickness is 1.5-4.0 mm.

The present invention will be further described with reference to examples and comparative examples.

Example 1

The invention relates to a titanium-containing weathering steel for a low-cost 650 MPa-level photovoltaic bracket and a preparation method thereof

The embodiment of the invention provides a hot rolled steel coil for a low-cost 650 MPa-level photovoltaic bracket. The production process comprises the following steps: billet steel, hot rolling, laminar cooling and coiling, wherein the chemical components of the billet steel are as follows by weight percent: c:0.06%, si:0.49%, mn:0.57%, P:0.12%, S:0.010%, cu:0.38%, cr:0.98%, ti:0.101%, N:0.0043%. The balance of Fe and unavoidable impurities.

The heating time in the hot rolling step is 62min, the thickness of a finish rolling inlet is 40mm, the finish rolling start temperature is 980 ℃, the finish rolling temperature is 885 ℃, the laminar cooling is the front cooling, the coiling temperature is 605 ℃, and the thickness is 4.0mm.

The tensile strength of the hot rolled steel coil for the photovoltaic bracket with 650MPa grade, which is produced by the method, is 705MPa, and the elongation is 26.0%.

Weather resistance index i=

26.01Cu+3.88Ni+1.2Cr+1.49Si+17.28P-7.92CuNi-9.1NiP-33.39CuCu＝9.04

Example two

The invention relates to titanium-containing weathering steel for a 650 MPa-level photovoltaic bracket and a preparation method thereof

The embodiment of the invention provides a hot rolled steel coil for a low-cost 650 MPa-level photovoltaic bracket. The production process comprises the following steps: billet steel, hot rolling, laminar cooling and coiling, wherein the chemical components of the billet steel are as follows by weight percent: c:0.08%, si:0.45%, mn:0.49%, P:0.09%, S:0.008%, cu:0.35%, cr:0.88%, ti:0.083%, N:0.0048%. The balance of Fe and unavoidable impurities.

The heating time in the hot rolling step is 80min, the thickness of a finish rolling inlet is 35mm, the finish rolling start temperature is 1050 ℃, the finish rolling temperature is 905 ℃, the laminar cooling is the front cooling, the coiling temperature is 635 ℃, and the thickness is 3.0mm.

The tensile strength of the hot rolled steel coil for the photovoltaic bracket with 650MPa grade and the elongation percentage of the hot rolled steel coil for the photovoltaic bracket with 650MPa grade produced by the method are 685MPa and 25.0 percent.

Weather resistance index i=

26.01Cu+3.88Ni+1.2Cr+1.49Si+17.28P-7.92CuNi-9.1NiP-33.39CuCu＝8.32

Example III

The invention relates to a titanium-containing weathering steel for a low-cost 650 MPa-level photovoltaic bracket and a preparation method thereof

The embodiment of the invention provides a hot rolled steel coil for a low-cost 650 MPa-level photovoltaic bracket. The production process comprises the following steps: billet steel, hot rolling, laminar cooling and coiling, wherein the chemical components of the billet steel are as follows by weight percent: c:0.07%, si:0.36%, mn:0.41%, P:0.083%, S:0.006%, cu:0.27%, cr:0.77%, ti:0.066%, N:0.0040%. The balance of Fe and unavoidable impurities.

In the hot rolling step, the thickness of a finish rolling inlet is 30mm, the finish rolling start temperature is 1077 ℃, the finish rolling temperature is 918 ℃, the laminar cooling is the front cooling, the coiling temperature is 655 ℃, and the thickness is 1.5mm.

The tensile strength of the hot rolled steel coil for the low-cost 650 MPa-level photovoltaic bracket produced by the method is 683MPa, and the elongation is 23.5%.

Weather resistance index i=

26.01Cu+3.88Ni+1.2Cr+1.49Si+17.28P-7.92CuNi-9.1NiP-33.39CuCu＝7.54

Comparative example one

Specific reference is made to a hot rolled steel coil for 550 MPa-level solar support and a production method thereof

Example 1 in (CN 113528949A)

A hot rolled steel coil for a 550MPa grade solar bracket comprises the following chemical components: 0.03% of C, 0.1% of Si, 1.20% of Mn, 0.025% of P, 0.015% of S, 0.1% of Cu, 0.4% of Cr, 0.015% of Nb, 0.01% of V, 0.02% of Als and the balance of iron and unavoidable impurities.

The preparation method comprises the following steps: the molten iron is processed into a continuous casting slab with the same chemical composition as the hot rolled steel coil for the 550MPa grade solar bracket through the working procedures of 150t converter vanadium extraction, 150t converter smelting, LF refining and continuous casting, and the thickness of the continuous casting slab is 190mm; heating the continuous casting slab in a heating furnace at 1200 ℃ for 120min, discharging the continuous casting slab from the heating furnace, performing high-pressure water descaling, performing rough rolling for 7 times by a roughing mill, wherein the thickness of an intermediate billet is 33mm, the outlet temperature of the roughing mill is 1080 ℃, performing rolling for 6 times by a hot rolling box, performing finishing rolling for 6 times by a finishing rolling machine, the outlet temperature of the finishing rolling machine is 860 ℃, the rolling reduction rate of the last rolling of the finishing rolling is 18%, and performing concentrated cooling for the front section, and coiling at 600 ℃ to obtain a hot rolled steel coil for the solar bracket, wherein the thickness of the hot rolled steel coil is 3.0mm and the width of the hot rolled steel coil is 1250 mm.

The tensile strength of the product is 610MPa and the elongation is 23.0 percent through detection.

Weather resistance index

I＝26.01Cu+3.88Ni+1.2Cr+1.49Si+17.28P-7.92CuNi-9.1NiP-33.39CuCu＝3.33

Comparative example two

Specific reference is made to "weathering steel for photovoltaic supports and method for producing same" (CN 114438411A)

Example 1

A weather-resistant steel for a photovoltaic bracket comprises the following chemical components: 0.061% of C, 0.36% of Si, 0.55% of Mn, 0.011% of P, less than or equal to 0.002% of S, 0.30% of Cu, 0.50% of Cr, 0.15% of Ni, 0.015% of Nb, 0.013% of Ti, 0.0049% of N, 0.0015% of Ca and the balance of iron and unavoidable impurities.

The preparation method comprises the following steps: smelting qualified molten steel through a molten iron pretreatment, a top-bottom combined blown converter, LF external refining and an RH vacuum degassing furnace, wherein the final sulfur of the molten iron pretreatment is 9ppm; top-bottom combined blown converter endpoint oxygen 310ppm; refining and making white slag outside an LF furnace, keeping the white slag for 20min, performing Ca treatment improvement and promoting floating of inclusions, and performing soft stirring by adopting argon for 11min; the RH vacuum degassing furnace has a vacuum degree of 60pa and a holding time of 18min; continuously casting molten steel into a 210mm plate blank; heating the steel billet to 1210 ℃ for 155min, so as to ensure the sufficient solid solution of alloy elements; rolling by adopting a TMCP process, wherein the rolling temperature of a recrystallization zone is 1085 ℃, the total deformation rate is 74%, the starting temperature of an austenite non-recrystallization zone is 970 ℃, the total deformation is 79.3%, and the control interval of the final rolling temperature is 910 ℃, so that the precipitation of high Wen Xian eutectoid ferrite is avoided; rapidly feeding water after rolling is finished, wherein the cooling rate is 25 ℃/s, and cooling to 640 ℃; and (3) feeding the hot coil into a slow cooling pit at 590 ℃ for slow cooling so as to fully release the internal stress generated by rolling deformation and phase change, discharging from the slow cooling pit after 48 hours, and cooling to room temperature.

The tensile strength of the product is 451MPa and the elongation is 28.5 percent.

Weather resistance index

I＝26.01Cu+3.88Ni+1.2Cr+1.49Si+17.28P-7.92CuNi-9.1NiP-33.39CuCu＝6.37

Comparative example three

Specific reference is made to example 1 of a high-strength corrosion-resistant cold-resistant hot rolled steel coil, a method for producing the same and applications thereof (CN 113652599B)

A high-strength corrosion-resistant cold-resistant hot rolled steel coil comprises the following chemical components: 0.15% of C, 0.1% of Si, 0.025% of Mn, 0.020% of P, 0.010% of S, 0.1% of Cu, 0.3% of Cr, 0.01% of V, 0.025% of Ti, 0.02% of Als, and the balance of iron and unavoidable impurities.

The preparation method comprises the following steps: extracting vanadium by a 150t converter, smelting by the 150t converter, LF refining and continuous casting to obtain a slab with the thickness of 200 mm; heating the slab in a heating furnace for 120min at 1200 ℃; discharging the slab from the heating furnace, and removing scales by high-pressure water with the pressure of 20 MPa; rolling the slab through a roughing mill for 5 times, wherein the outlet temperature of roughing rolling is 1040 ℃; and then passing the slab through a hot rolling box, finishing the slab through a finishing mill for 7 times, wherein the outlet temperature of finish rolling is 860 ℃, then carrying out dispersed cooling and coiling at 580 ℃, and obtaining the high-strength corrosion-resistant cold-resistant hot rolled steel coil with the thickness of 3.0mm and the width of 1250 mm.

The tensile strength of the product is 460MPa and the elongation is 26.0 percent through detection.

Weather resistance index

I＝26.01Cu+3.88Ni+1.2Cr+1.49Si+17.28P-7.92CuNi-9.1NiP-33.39CuCu＝3.12

The preparation method of the embodiment of the invention is simple, the strength level is higher, and the weather resistance index is larger as can be seen by combining the preparation methods, the mechanical properties and the weather resistance index of the embodiment and the comparative embodiment. Therefore, the titanium-containing weathering steel for the low-cost 650 MPa-level photovoltaic bracket and the preparation method thereof disclosed by the invention have the advantages of simple and feasible process steps, high strength, favorable light weight and good corrosion resistance, and have good application prospects.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims (4)

1. The titanium-containing weathering steel for the low-cost 650 MPa-level photovoltaic bracket is characterized by comprising the following chemical components in percentage by weight: c: less than or equal to 0.08 percent, si:0.35 to 0.50 percent, mn:0.40 to 0.60 percent, P:0.08 to 0.12 percent, S: less than or equal to 0.010 percent, cu:0.25 to 0.40 percent, cr:0.75% -1.00%, ti:0.065% -0.105%, N: less than or equal to 0.0050 percent, and the balance of Fe and unavoidable impurities.

2. The low-cost 650 MPa-grade titanium-containing weathering steel for photovoltaic brackets according to claim 1, wherein the tensile strength of the prepared hot rolled steel coil is not less than 650MPa, and the weathering index I is not less than 7.5.

3. A method for preparing the titanium-containing weathering steel for the low-cost 650 MPa-level photovoltaic brackets according to claim 1 or 2, characterized by comprising the steps of hot rolling, cooling and coiling:

wherein the heating time in the hot rolling step is 60-100 min;

the thickness of a finish rolling inlet in the hot rolling step is 30 mm-40 mm,

the initial rolling temperature of the finish rolling is 980-1080 ℃,

the final rolling temperature in the hot rolling step is 880-920 ℃;

in the cooling step, the laminar cooling is front-stage cooling; the temperature in the coiling step is 600-660 ℃.

4. The method for producing a titanium-containing weathering steel for low-cost 650 MPa-grade photovoltaic brackets according to claim 3, characterized in that the coiling thickness is 1.5mm to 4.0mm.