A high-strength and high-weather-resistance steel for a photovoltaic support and a manufacturing method thereof

Abstract

The present invention belongs to the technical field of weathering steel, and discloses a high-strength and high-weathering steel for photovoltaic brackets and a manufacturing method thereof. Its chemical composition and weight percentage content are as follows: C: 0.06 - 0.08%, Si: 0.15 - 0.25%, Mn: 0.45 - 0.55%, P: ≤0.015%, S: ≤0.003%, Cu: 0.2 - 0.3%, Als: 0.02 - 0.05%, Ti: 0.09 - 0.12%, Cr: 2.4 - 2.6%, N ≤0.005%, B ≤0.0005%, Nb ≤0.01%, V ≤0.015%, Ni ≤0.10%, Mo ≤0.10%, and the balance is Fe and inevitable inclusions. The present invention combines the process technologies of high-weathering steel and high-strength steel, realizes high weathering performance by using high Cr, economically obtains high strength by using high Ti precipitation strengthening, overcomes the contradiction between ferrite phase transformation caused by high alloy and Ti precipitation strengthening, overcomes the influence of composition adjustment on the quality of continuous casting billets, realizes "doubling the strength and doubling the service life" compared with ordinary weathering steel, and at the same time has the significant advantages of high elongation and high formability.

Description

Technical Field

[0001] The present invention belongs to the technical field of weathering steel, and particularly relates to a high-strength and high-weathering steel for photovoltaic brackets and a manufacturing method thereof. Background Art

[0002] Photovoltaic brackets are the main structures to ensure the efficient, stable, and safe operation of solar panels, playing a role in supporting and protecting the system. They are prone to corrosion failure when directly facing natural environmental erosion. For this reason, the steel used for photovoltaic brackets is mainly made of low-grade steel types (such as Q345) by hot-dip galvanizing. The production process is long, the pollution is serious, and the strength is low, and the coating is easy to peel off, which cannot meet the requirements of the whole life cycle of photovoltaic projects. Regular maintenance and renovation are also required in the later stage. Therefore, low strength, short life, high pollution, and high cost have become the bottlenecks restricting the steel for photovoltaic brackets.

[0003] The photovoltaic industry has become a new track for green and low-carbon development. The research and application of energy-saving and environmental protection materials are imminent. The application of weathering steel in the photovoltaic industry will surely become a trend. However, the existing weathering steel for photovoltaic brackets cannot well balance high weathering performance, high strength, long service life, and low cost. Some have too high costs, adding a large amount of expensive alloys such as Mo, Nb, V, and Ni. Some steels cannot meet the requirements of actual applications in terms of mechanical properties such as corrosion resistance, yield strength, and tensile strength. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a high-strength and high-weathering steel for photovoltaic brackets and a manufacturing method thereof in view of the deficiencies of the existing technology. By combining the process technologies of high-weathering steel and high-strength steel, high Cr is used to achieve high weathering performance, and high Ti is used for precipitation strengthening to economically obtain high strength. The contradiction between ferrite phase transformation caused by high alloy and Ti precipitation strengthening is overcome, and the influence of composition adjustment on the quality of continuous casting billets is overcome, realizing "doubling the strength and doubling the life" compared with ordinary weathering steel, and at the same time having the advantages of high elongation and high formability.

[0005] To solve the technical problems proposed by the present invention, the present invention provides a high-strength and high-weathering steel for photovoltaic brackets, and its chemical composition and weight percentage content are as follows: C: 0.06 - 0.08%, Si: 0.15 - 0.25%, Mn: 0.45 - 0.55%, P: ≤0.015%, S: ≤0.003%, Cu: 0.2 - 0.3%, ALs: 0.02 - 0.05%, Ti: 0.09 - 0.12%, Cr: 2.4 - 2.6%, N ≤0.005%, B ≤0.0005%, Nb ≤0.01%, V ≤0.015%, Ni ≤0.1%, Mo ≤0.1%, and the balance is Fe and inevitable inclusions.

[0006] Preferably, the chemical composition and weight percentage of the high-strength and highly weather-resistant steel for the photovoltaic support are as follows: C: 0.065 - 0.075%, Si: 0.18 - 0.22%, Mn: 0.48 - 0.53%, P: ≤0.012%, S: ≤0.002%, Cu: 0.23 - 0.28%, Als: 0.02 - 0.03%, Ti: 0.1 - 0.11%, Cr: 2.45 - 2.55%, N ≤0.004%, B ≤0.0004%, Nb ≤0.008%, V ≤0.008%, Ni ≤0.05%, Mo ≤0.05%, and the balance is Fe and inevitable inclusions.

[0007] In the above solution, the yield strength of the high-strength and highly weather-resistant steel for the photovoltaic support is 680 - 780 MPa, the tensile strength is 800 - 900 MPa, the elongation after fracture A ≥ 15%, the corrosion rate is only less than 40% of that of Q345B steel, and the service life can reach more than 25 years.

[0008] The present invention also provides a manufacturing method for the high-strength and highly weather-resistant steel for the photovoltaic support, including the following steps:

[0009] 1) The hot metal is pretreated by KR desulfurization to control the S content in the hot metal ≤0.001%;

[0010] 2) The hot metal is smelted in a converter, the end temperature of the converter is 1620 - 1645°C, the O content of the molten steel at the end is controlled to be 0.04 - 0.06%, the C content ≤0.045%, and the B content ≤0.0001%;

[0011] 3) Ferro-aluminum is added for complete deoxidation when tapping from the converter, the Als content of the molten steel is controlled to be 0.015 - 0.035%, and alloying is carried out according to the chemical composition of the steel; the slag volume when tapping ≤40 mm;

[0012] 4) The molten steel is blown with argon at the bottom of the argon blowing station to control the Als content in the molten steel to be 0.03 - 0.05%;

[0013] 5) The molten steel is deeply desulfurized in an LF furnace, the LF smelting time ≤40 min, the S content in the molten steel at the station is controlled to be ≤0.002%, the B content ≤0.0003%, and the Als content is 0.03 - 0.05%;

[0014] 6) The molten steel is subjected to RH vacuum cyclic degassing, the vacuum degree ≤20 Pa, the vacuum cyclic time is 30 - 38 min, and the temperature at the end of vacuum is 1549 - 1559°C;

[0015] 7) The molten steel is continuously cast into slabs, the superheat of the molten steel during continuous casting is 6 - 11°C, the tundish temperature is 1525 - 1530°C, and the casting speed is 0.9 - 1.4 m / min;

[0016] 8) The slab is heated, rolled, and coiled to obtain high-strength and highly weather-resistant steel for photovoltaic brackets.

[0017] In the above solution, the ferrochrome added during the alloying process is low-boron and low-carbon ferrochrome, with a Cr content of 57-58%, a B content ≤ 0.001%, a C content of 0.2-0.25%, and an addition amount of 43-48 kg per ton of steel.

[0018] In the above solution, low-boron magnesia-carbon bricks are used at the ladle slag line of the LF furnace, and the B content of the low-boron magnesia-carbon bricks ≤ 0.2%.

[0019] In the above solution, aluminum pellets are added for slag formation during the early stage of deep desulfurization treatment in the LF furnace, and when the S content of the molten steel is reduced to below 0.002%, aluminum wire is fed instead.

[0020] In the above solution, a mold with a taper of 1.2-1.24% is used during the continuous casting process. The cooling water flow rate on the wide face of the mold is 3250-3450 L / min, and the cooling water flow rate on the narrow face is 610-630 L / min.

[0021] In the above solution, the mold powder used during the continuous casting process is a special slag for ultra-low carbon steel, with an alkalinity of 0.86-0.96, a viscosity of 0.38-0.48 Pa·S (at a temperature of 1300 °C), and a melting point of 1130-1190 °C.

[0022] In the above solution, the temperature for heating the slab is 1280-1320 °C; the rough rolling in the rolling process ends at 1100-1140 °C, and the finish rolling ends at 870-910 °C; the coiling temperature is 600-640 °C.

[0023] The components and their content ranges in the present invention are mainly based on the following principles:

[0024] C: A conventional strengthening element, which can increase the yield strength and tensile strength. However, too high carbon content will reduce plasticity and impact toughness. The more suitable addition amount of carbon is 0.06-0.08%, preferably 0.065-0.075%.

[0025] Mn: Manganese dissolves in ferrite, raising the critical temperature, greatly reducing the martensite transformation temperature of the steel and the phase transformation rate in the steel, improving the hardenability of the steel and increasing the retained austenite content, making the quenched and tempered structure of the steel uniform and refined. However, too high manganese content will increase the overheating sensitivity and temper brittleness of the steel. The more suitable addition amount of manganese is 0.45-0.55%, preferably 0.48-0.53%.

[0026] Si: During the steelmaking process, it can be used as a reducing agent and deoxidizer, which can improve the strength and hardness of steel. When steel containing silicon is heated in an oxidizing atmosphere, a SiO2 film will form on the surface, thereby improving the oxidation resistance of steel at high temperatures. However, the silicon content should not be too high, as it will reduce plasticity and weldability. The more suitable addition amount of silicon is 0.15 - 0.25%, preferably 0.18 - 0.22%.

[0027] Cr: It can significantly improve the strength and hardness of steel, enhance the oxidation resistance and corrosion resistance of steel, reduce the critical cooling rate of steel, and improve the hardenability of steel. Chromium can form a relatively dense protective layer on the surface of steel, playing a role in protecting the matrix and effectively improving the weather resistance of steel. However, when the chromium content in steel is too high, the toughness of the steel plate will deteriorate, reducing the weldability of steel. The more suitable addition amount of chromium is 2.4 - 2.6%, preferably 2.45 - 2.55%.

[0028] Cu: It can significantly improve the corrosion resistance of steel, increase the strength of steel without having an adverse effect on weldability. However, when the content is relatively high, it is not conducive to hot deformation processing and causes copper embrittlement during hot deformation processing. The more suitable addition amount of copper is 0.2 - 0.3%, preferably 0.23 - 0.28%.

[0029] Ti: Titanium is one of the strong ferrite - forming elements, which reduces the austenite phase region. When the titanium content is relatively high, TiFe2 is formed and precipitated dispersedly, and precipitation strengthening can double the strength of steel compared with that of conventional support steel. Titanium has a very strong affinity with nitrogen, oxygen, and carbon, and it is a good deoxidizing and degassing agent and an effective element for fixing nitrogen and carbon. The TiC formed by titanium and carbon has high stability, and TiC particles can prevent the grains of steel from growing and coarsening, playing a role in refining grains. However, when the titanium content is too high, the toughness of steel will be reduced. The more suitable addition amount of titanium is 0.09 - 0.12%, preferably 0.1 - 0.11%.

[0030] Al: Aluminum has a very strong affinity with oxygen and nitrogen and is a deoxidizing and nitrogen - fixing agent during steelmaking. Aluminum can reduce the austenite phase region in steel. Aluminum can refine the essential grains of steel and increase the temperature at which the grains of steel coarsen. However, when the content of dissolved aluminum in steel is too high, the austenite grains are prone to grow and coarsen instead. The more suitable addition amount of aluminum is 0.02 - 0.05%, preferably 0.02 - 0.03%.

[0031] B: For the steel used in photovoltaic supports, a small amount of B in the steel plate will cause the hardness of the weld seam to be high after welding, making the steel for photovoltaic supports prone to fatigue cracks during long - term service, seriously affecting the service life. And problems are also likely to occur during the welding process. Therefore, in the present invention, it is required that B ≤ 0.0005%, preferably B ≤ 0.0004%.

[0032] The object of the present invention is to obtain high strength and high weather resistance at low cost. The Ti element added in the present invention is relatively high, and the precipitation strengthening of Ti doubles the strength of the steel at a relatively low cost. Higher Cr and Cu elements are added to achieve the high weather resistance of the steel plate. However, when the contents of Cr, Cu, and Ti are all relatively high, it is easy to cause ferrite phase transformation, which is contradictory to the precipitation strengthening of Ti. Because the conventional Ti strengthening principle is that titanium dissolves in the γ and α phases or austenite phase to form a solid solution to achieve the purpose of solid solution strengthening. Its disadvantage is that when the titanium content is high, the toughness of the steel is reduced, and when the titanium content is low, the solid solution strengthening cannot reach the required high strength.

[0033] To overcome this contradiction and achieve a significant strengthening effect while improving the weather resistance, different from solid solution strengthening, it is achieved through the interphase precipitation strengthening of Ti. When Ti reaches 0.09 - 0.12%, the structure of the precipitates can be complete and the density can be relatively high, which can effectively limit the movement of dislocations during the plastic processing. In ferrite, during the transformation of γ iron to α iron, the alloy carbides continuously aggregate at the interface between the migrating austenite and ferrite, resulting in the appearance of special carbides arranged parallel to the γ / α interface. The combined action of the grain-refined ferrite phase and the special carbides arranged parallel to the γ / α interface, and by controlling the layer spacing, particle spacing, and carbide radius of the carbides under a certain carbide volume fraction, the strength of the steel can be increased.

[0034] The regulation of the manufacturing process of the present invention is mainly based on the following principles:

[0035] The difficulty in the manufacturing process of the present invention lies in controlling the B content in the molten steel. 1) During the converter smelting process, the top-bottom combined blowing in the converter utilizes the strong deboronation effect of blowing oxygen in the converter. Under the strong oxidation effect, the boron in the molten steel is fully oxidized and enters the slag as oxidation products, controlling the B in the molten steel ≤ 0.0001%. 2) During the tapping process of the converter, strictly control the slag entrainment amount ≤ 40 mm. 3) Since the steel of the present invention has a high chromium content, a large amount of ferrochromium alloy is added during the alloying process. The alloy contains a certain amount of B impurity element, resulting in an increase in the B element in the molten steel. Therefore, low-boron and low-carbon ferrochromium is selected to prevent the excessive addition of ferrochromium alloy from causing the boron and carbon contents in the molten steel to exceed the standard. 4) Although the slag entrainment amount is strictly controlled during the tapping process of the converter, a part of the converter slag will still enter the ladle. During the deep desulfurization treatment of the molten steel in the LF furnace, a part of the boron will return to the molten steel, increasing the boron content in the molten steel. Controlling the return of boron in the slag to the molten steel is a difficult point. Therefore, aluminum pellets are used to make the reducing slag for desulfurization. The aluminum pellets are added in the early stage of desulfurization. When the sulfur is reduced to below 0.002%, an aluminum wire is fed through the slag layer directly by a wire feeder to avoid the further reduction of the B element in the slag to the molten steel when adding aluminum pellets through the slag layer. 5) Control the dosage of the boron-containing additive in the magnesia-carbon brick at the slag line of the ladle to make the B content in the magnesia-carbon brick ≤ 0.2%, preventing the severe erosion of the slag line of the ladle during the smelting of the molten steel in the ladle furnace, resulting in the decomposition of the magnesia-carbon brick and bringing the boron element contained therein into the molten steel, increasing the B content in the molten steel, and controlling the smelting time of the LF furnace ≤ 40 minutes to reduce the erosion of the molten steel on the slag line of the ladle. Finally, control the B in the molten steel at the end of the LF furnace production ≤ 0.0003%.

[0036] Another difficulty in the manufacturing process of the present invention lies in controlling the quality of the continuous casting billet. The steel of the present invention contains a relatively high Ti content. Ti has a great affinity for N and O and is extremely easy to form TiN and TiO2 inclusions. The non-metallic inclusions formed during the smelting process are not easy to separate and float up and remove, thus affecting the purity of the molten steel. Longitudinal cracks, edge cracks, segregation, surface scabs, pits and other defects are likely to occur in the continuous casting billet, easily scrapping the continuous casting billet. Therefore, on the one hand, strictly control the process parameters of the vacuum refining process, which can reduce the nitrogen content in the steel, remove harmful impurities and gases, and improve the purity of the molten steel, thereby improving the strength and weather resistance of the steel; on the other hand, strictly control the parameters of the continuous casting steady casting, use a mold powder with high alkalinity, high viscosity and high melting point, and adopt a low superheat and low casting speed, which can significantly reduce the quality defects of the continuous casting billet.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] The present invention combines the process technologies of high weathering steel and high-strength steel, realizes high weathering performance by using high Cr, economically obtains high strength by precipitation strengthening with high Ti, overcomes the contradiction between ferrite phase transformation caused by high alloy and Ti precipitation strengthening, overcomes the influence of composition adjustment on the quality of continuous casting billets, realizes "doubling the strength and doubling the service life" compared with ordinary weathering steel, and at the same time has the remarkable advantages of high elongation and high formability. The yield strength of the high-strength and high-weathering steel for photovoltaic brackets obtained is 680-780 MPa, the tensile strength is 800-900 MPa, the elongation after fracture A≥15%, the corrosion rate is only less than 40% of that of Q345B steel, and the service life can reach more than 25 years. Detailed implementation manners

[0039] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments.

[0040] In the following embodiments, the ferrochrome added during the alloying process is low-boron and low-carbon ferrochrome, with a Cr content of 57.6%, a B content of 0.0008%, and a C content of 0.23%; while in the comparative example, the ferrochrome added during the alloying process is medium-carbon ferrochrome, with a Cr content of 53.7%, a B content of 0.004%, and a C content of 1%.

[0041] In the following embodiments, low-boron magnesia-carbon bricks are used at the slag line of the LF furnace ladle, with a B content of 0.15%; while in the comparative example, medium-boron magnesia-carbon bricks are used at the slag line of the LF furnace ladle, with a B content of 0.8%.

[0042] Examples 1-10 and Comparative Examples 1-2

[0043] The chemical compositions and weight percentage contents of the steels in each example and comparative example are shown in Tables 1 and 2.

[0044] Table 1 Chemical composition of steel I (wt, %)

[0045] Serial number C Si Mn P S Cu ALs Ti Example 1 0.065 0.16 0.47 0.008 0.0012 0.2 0.022 0.09 Example 2 0.07 0.18 0.48 0.014 0.0015 0.22 0.03 0.095 Example 3 0.075 0.2 0.5 0.009 0.0009 0.23 0.025 0.1 Example 4 0.08 0.17 0.51 0.013 0.001 0.24 0.018 0.102 Example 5 0.068 0.22 0.52 0.011 0.002 0.25 0.02 0.105 Example 6 0.062 0.25 0.53 0.012 0.0022 0.26 0.028 0.108 Example 7 0.06 0.23 0.46 0.015 0.0025 0.2 0.032 0.11 Example 8 0.072 0.21 0.49 0.012 0.0018 0.27 0.035 0.115 Example 9 0.078 0.18 0.54 0.01 0.0028 0.29 0.038 0.118 Example 10 0.076 0.15 0.55 0.008 0.0011 0.3 0.04 0.12 Comparative example 1 0.095 0.1 0.25 0.028 0.005 0.15 0.005 0.001 Comparative example 2 0.1 0.4 0.45 0.026 0.009 0.35 0.06 0.002

[0046] Table 2 Chemical composition of steel II (wt, %)

[0047] Serial number Cr N B Nb V Ni Mo Example 1 2.4 0.0035 0.00032 0.002 0.003 0.012 0.010 Example 2 2.42 0.004 0.00038 0.001 0.004 0.011 0.011 Example 3 2.44 0.0045 0.0004 0.003 0.001 0.008 0.006 Example 4 2.45 0.0041 0.00037 0.004 0.002 0.015 0.008 Example 5 2.5 0.0046 0.00035 0.002 0.003 0.013 0.013 Example 6 2.52 0.0038 0.00028 0.001 0.002 0.007 0.007 Example 7 2.54 0.0043 0.00046 0.003 0.005 0.006 0.012 Example 8 2.55 0.0037 0.00049 0.004 0.002 0.005 0.005 Example 9 2.58 0.0048 0.00036 0.001 0.003 0.004 0.009 Example 10 2.6 0.005 0.0005 0.003 0.004 0.01 0.014 Comparative example 1 1.5 0.0065 0.001 0.002 0.005 0.014 0.015 Comparative example 2 5.5 0.008 0.0015 0.003 0.004 0.02 0.021

[0048] The manufacturing method of the steel in each example includes the following steps:

[0049] 1) The hot metal is pretreated by KR desulfurization to control the S content of the hot metal;

[0050] 2) The hot metal is smelted in a converter to control the end-point temperature of the converter and the O, C, and B contents of the end-point molten steel;

[0051] 3) The converter tapping is completely deoxidized with ferrosilicon aluminum, and the Als content of the molten steel is controlled; alloying is carried out according to the chemical composition of the steel, and low-boron and low-carbon ferrochrome is added during the alloying process; the amount of slag carried over during tapping is controlled;

[0052] 4) The molten steel is blown with argon from the bottom at the argon blowing station to control the Als content of the molten steel;

[0053] 5) The molten steel is subjected to deep desulfurization treatment in the LF furnace. Low-boron magnesia-carbon bricks are used at the slag line of the LF furnace ladle. Aluminum pellets are added for slag formation in the early stage of desulfurization. When the S content of the molten steel is reduced to less than 0.002%, aluminum wire is fed instead; the LF smelting time, as well as the S, B, and Als contents of the molten steel at the end of tapping, are controlled;

[0054] 6) The molten steel is subjected to RH vacuum cyclic degassing, and the vacuum degree, vacuum cyclic time, and vacuum end temperature are controlled;

[0055] 7) The molten steel is continuously cast into slabs. The mold powder used in the mold is a special slag for ultra-low carbon steel, which has higher viscosity, alkalinity, and melting point compared to ordinary mold powder;

[0056] 8) The slab is heated and then rolled and coiled to obtain high-strength and high-weather-resistant steel for photovoltaic brackets.

[0057] The manufacturing process of each comparative steel is the same as that of the example, except for the control of parameters. The main process parameters of each example and comparative example are shown in Table 3-6.

[0058] Table 3 Control of the composition content of hot metal / molten steel during the manufacturing process (wt, %)

[0059]

[0060] Table 4 Parameters related to the mold and mold powder during continuous casting

[0061]

[0062]

[0063] Table 5 Other process parameters during the manufacturing process -

[0064]

[0065] Table 6 Other process parameters during the manufacturing process -

[0066]

[0067] The performance parameters of the steel in each example and comparative example were tested. Among them, in order to characterize the weather resistance of the steel, a cyclic immersion corrosion test was carried out in accordance with TB / T 2375-1993 "Test Method for Cyclic Immersion Corrosion of Weathering Steel for Railways". The specimens were alternately immersed in the corrosion medium and exposed to the air to simulate the corrosion behavior of the steel in the service environment, and the weight loss rate, that is, the corrosion rate, was measured. Specifically, specimens with dimensions of 50 mm × 25 mm × 3 mm were used, the immersion solution was 3.5% NaCl solution, and the remaining test conditions were the same as those in TB / T 2375-1993. The test cycle was 72 h, and the test results are shown in Table 7.

[0068] Table 7 Performance Test Results

[0069]

[0070] As can be seen from Table 7, compared with the currently conventional Q345 grade steel used for photovoltaic brackets, the high-strength and high-weather-resistant steel for photovoltaic brackets of the present invention has achieved "doubling of strength". The service life of the bare Q345B steel is generally only about 10 years and will terminate service due to reasons such as rust and corrosion. However, the corrosion rate of the steel of the present invention is less than 40% of that of Q345B steel. Therefore, the service life of the bare steel of the present invention can be as long as more than 25 years, achieving "doubling of life".

[0071] The above examples are merely examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here, and the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A manufacturing method of high-strength and high-weather resistance steel for a photovoltaic support, characterized in that, It includes the following steps: 1) The hot metal is pretreated by KR desulfurization to control the S content in the hot metal ≤ 0.001%; 2) Converter smelting, the converter end temperature is 1620 - 1645 °C, control the O content in the end molten steel to be 0.04 - 0.06%, C content ≤ 0.045%, B content ≤ 0.0001%; 3) Add ferrosilicon for complete deoxidation when tapping from the converter, control the Als content in the molten steel to be 0.015 - 0.035%, and alloy according to the chemical composition of the steel. Add ferrochrome with B content ≤ 0.001% during alloying; the slag volume during tapping ≤ 40 mm; 4) The molten steel is bottom-blown with argon in the argon blowing station to control the Als content in the molten steel to be 0.03 - 0.05%; 5) The molten steel is deeply desulfurized by LF furnace. The LF smelting time ≤ 40 min. Add aluminum pellets for slag formation in the early stage of desulfurization. When the S content in the molten steel is reduced to below 0.002%, change to feeding aluminum wire. Control the S content in the molten steel ≤ 0.002%, B content ≤ 0.0003%, and Als content to be 0.03 - 0.05% when leaving the station; 6) The molten steel is subjected to RH vacuum circulation degassing, the vacuum degree ≤ 20 Pa, the vacuum circulation time is 30 - 38 min, and the temperature at the end of vacuum is 1549 - 1559 °C; 7) The molten steel is continuously cast into slabs. During continuous casting, the superheat of the molten steel is 6 - 11 °C, the tundish temperature is 1525 - 1530 °C, and the casting speed is 0.9 - 1.4 m / min; the basicity of the mold powder is 0.86 - 0.96, the viscosity is 0.38 - 0.48 Pa·S, and the melting point is 1130 - 1190 °C; 8) The slab is heated and then rolled and coiled to obtain high-strength and high-weather-resistant steel for photovoltaic brackets. Its chemical composition and weight percentage content are: C: 0.06 - 0.08%, Si: 0.15 - 0.25%, Mn: 0.45 - 0.55%, P: ≤ 0.015%, S: ≤ 0.003%, Cu: 0.2 - 0.3%, Als: 0.02 - 0.05%, Ti: 0.09 - 0.12%, Cr: 2.4 - 2.6%, N ≤ 0.005%, B ≤ 0.0005%, Nb ≤ 0.01%, V ≤ 0.015%, Ni ≤ 0.1%, Mo ≤ 0.1%, and the balance is Fe and unavoidable inclusions.

2. The manufacturing method of the high-strength and high-weather resistance steel for a photovoltaic support according to claim 1, characterized in that, The chemical composition and weight percentage content of the high-strength and high-weather-resistant steel for photovoltaic brackets are: C: 0.065 - 0.075%, Si: 0.18 - 0.22%, Mn: 0.48 - 0.53%, P: ≤ 0.012%, S: ≤ 0.002%, Cu: 0.23 - 0.28%, Als: 0.02 - 0.03%, Ti: 0.1 - 0.11%, Cr: 2.45 - 2.55%, N ≤ 0.004%, B ≤ 0.0004%, Nb ≤ 0.008%, V ≤ 0.008%, Ni ≤ 0.05%, Mo ≤ 0.05%, and the balance is Fe and unavoidable inclusions.

3. The manufacturing method of the high-strength and high-weather resistance steel for a photovoltaic support according to claim 1, wherein, The yield strength of the high-strength and high-weathering steel for photovoltaic support is 680 - 780 MPa, the tensile strength is 800 - 900 MPa, the elongation after fracture A ≥ 15%, the corrosion rate is only less than 40% of that of Q345B steel, and the service life can reach more than 25 years.

4. The manufacturing method of the high-strength and high-weather-resistant steel for a photovoltaic support according to claim 1, characterized in that, The ferrochrome added in the alloying process is low-boron and low-carbon ferrochrome, with a Cr content of 57 - 58%, a B content ≤ 0.001%, a C content of 0.2 - 0.25%, and the addition amount is 43 - 48 kg per ton of steel.

5. The manufacturing method of the high-strength and high-weather-resistant steel for a photovoltaic support according to claim 1, characterized in that, Low-boron magnesia-carbon bricks are used at the ladle slag line of the LF furnace, and the B content of the low-boron magnesia-carbon bricks ≤ 0.2%.

6. The manufacturing method of the high-strength and high-weather-resistance steel for a photovoltaic support according to claim 1, wherein, In the continuous casting process, a mold with a taper of 1.2 - 1.24% is used. The cooling water flow rate on the wide face of the mold is 3250 - 3450 L / min, and the cooling water flow rate on the narrow face is 610 - 630 L / min.

7. The manufacturing method of the high-strength and high-weather-resistance steel for a photovoltaic support according to claim 1, wherein The temperature of slab heating is 1280 - 1320 °C; in the rolling process, rough rolling ends at 1100 - 1140 °C, and finish rolling ends at 870 - 910 °C; the coiling temperature is 600 - 640 °C.

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