High-corrosion-resistance low-alloy steel for photovoltaic support and manufacturing method of high-corrosion-resistance low-alloy steel

Abstract

The invention discloses high-corrosion-resistance low-alloy steel for a photovoltaic support and a manufacturing method of the high-corrosion-resistance low-alloy steel. The technical problems that the manufacturing cost is high, the comprehensive performance is poor, and the production efficiency is low are solved. The high-corrosion-resistance low-alloy steel comprises the following components in percentage by mass: 0.11%-0.13% of C, 0.65%-0.79% of Si, 0.31%-0.50% of Mn, 0.020%-0.030% of P, 0.0041%-0.0049% of S, 3.7%-3.9% of Cr, 0.13%-0.18% of Cu, 0.08%-0.12% of Alt, less than or equal to 0.015% of Sn, less than or equal to 0.025% of As, less than or equal to 0.015% of Sb and the balance of Fe and inevitable impurities. The high-corrosion-resistance low-alloy steel meets the conditions that Sn + As + Sb is less than or equal to 0.050% and (Sn + As + Sb) / Cu is less than or equal to 0.28. The manufacturing method of the high-corrosion-resistance low-alloy steel comprises the steps of smelting, continuous casting, continuous casting billet heating, heat preservation, rough rolling, finish rolling, cooling and coiling. The manufacturing cost can be reduced, the steel performance is improved, and the production efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled steel strip manufacturing, and specifically relates to a high-corrosion-resistant low-alloy steel for a photovoltaic support and a manufacturing method thereof. Background Art

[0002] In recent years, guided by the goal of clean energy transformation, the development of renewable energy has been unstoppable. Solar energy has significant advantages such as being clean, safe, inexhaustible and inexhaustible. Photovoltaic power generation is the fastest-growing power generation technology, and its incremental power generation accounts for a steadily increasing proportion of the global total power generation.

[0003] Photovoltaic brackets are special equipment installed in photovoltaic power stations to support, fix and rotate photovoltaic modules. They are the link with the most consumables in the photovoltaic industry chain. Photovoltaic power stations are developing in a high-power trend, with increased module weight and bracket load. They are mostly built in harsh and changeable environments such as deserts, Gobi, wastelands, and saline-alkali lands, which place extremely high demands on the weight, bearing capacity, corrosion resistance, and stability of photovoltaic brackets.

[0004] At present, photovoltaic brackets are mainly based on plain carbon steel, and hot-dip galvanizing or zinc-aluminum-magnesium is used to improve the corrosion resistance of photovoltaic brackets. However, the production process of photovoltaic brackets has problems such as polluting the environment, increasing production steps, extending the process flow, and increasing manufacturing costs. In addition, during the transportation, processing, and installation of photovoltaic brackets, the coating on the surface is easily damaged, causing corrosion of the substrate, and post-maintenance is necessary to avoid premature failure.

[0005] Moreover, most of the weathering steels used in photovoltaic brackets in the prior art contain relatively high levels of precious metal elements, which increases production costs, and the overall performance of the steel is relatively poor. There are also problems such as high production difficulty and low production efficiency, which need to be improved. Summary of the invention

[0006] In order to solve all or part of the above problems, the purpose of the present invention is to provide a high corrosion-resistant low-alloy steel for photovoltaic brackets and a manufacturing method thereof, which can reduce manufacturing costs, achieve lightweight, and improve the comprehensive performance of steel, while also reducing production difficulty and improving production efficiency.

[0007] In a first aspect, the present invention provides a high corrosion resistant low alloy steel for a photovoltaic bracket, wherein the composition of the high corrosion resistant low alloy steel includes, by mass percentage: C: 0.11%-0.13%, Si: 0.65%-0.79%, Mn: 0.31%-0.50%, P: 0.020%-0.030%, S: 0.0041%-0.0049%, Cr: 3.7%-3.9%, Cu: 0.13%-0.18%, Alt: 0.08%-0.12%, Sn≤0.015%, As≤0.025%, Sb≤0.015%, and the rest is Fe and unavoidable impurities;

[0008] The high corrosion resistant low alloy steel satisfies Sn+As+Sb≤0.050%, (Sn+As+Sb) / Cu≤0.28.

[0009] Optionally, the high corrosion resistant low alloy steel has the following properties:

[0010] Yield strength ≥620MPa, tensile strength ≥750MPa, elongation after fracture ≥19%, 180°d=a cold bending test qualified;

[0011] After 72 hours of periodic immersion in a mixed solution of NaHSO3 and 3.5% NaCl with an initial concentration of 0.01 mol / L, the corrosion rate is ≤30% relative to Q355B ordinary steel, and the corrosion rate is ≤50% relative to Q450NQR1 general weathering steel.

[0012] In a second aspect, the present invention provides a method for manufacturing high corrosion resistant low alloy steel, comprising the following steps:

[0013] S1, through hot metal pretreatment desulfurization, top and bottom composite blowing converter smelting, LF refining and slab continuous casting, to obtain a continuous casting billet with a thickness of 180-230mm;

[0014] S2, loading the continuous casting billet into a walking beam heating furnace for heating and heat preservation;

[0015] S3, rolling the continuous casting slab by a rough rolling mill to obtain a strip;

[0016] S4, rolling the strip with a finishing mill to obtain a hot-rolled steel strip;

[0017] S5, the hot rolled steel strip is cooled during transportation on a laminar cooling roller;

[0018] S6, coiling the hot-rolled steel strip into a hot-rolled steel coil by a coiler.

[0019] Optionally, in S2, the temperature of the continuous casting billet out of the furnace is controlled to be 1180°C-1200°C, and the cumulative residence time in the furnace is controlled to be 180-210 minutes.

[0020] Optionally, in S3, the continuous casting billet is rough rolled by 7 rough rolling passes, and the rough rolling start temperature is controlled to be 1130°C-1150°C, the rough rolling finish temperature is controlled to be 1060°C-1100°C, and the strip thickness is controlled to be 28-40 mm.

[0021] Optionally, in S3, the absolute reduction of each rough rolling pass is: 35.1-37.3mm, 32.1-34.3mm, 28.4-32.7mm, 28-30.9mm, 23.6-26.7mm, 21.7-25.3mm, 21-24.2mm.

[0022] Optionally, in S4, the strip is finish-rolled by a 7-stand finishing mill, and the finishing rolling start temperature is controlled to be 1000°C-1050°C, the finishing rolling final temperature is controlled to be 850°C-890°C, and the thickness of the hot-rolled steel strip is controlled to be 1.5-4.0 mm.

[0023] Optionally, in S4, the absolute reduction of each finishing rolling stand is: 14.31-18.64mm, 5.57-8.95mm, 2.44-4.47mm, 1.28-2.46mm, 0.80-1.5mm, 0.36-0.9mm, 0.17-0.64mm respectively.

[0024] Optionally, in S5, the cooling method of the hot-rolled steel strip on the laminar cooling roller is rear-stage cooling, and the flow ratio of the upper and lower header cooling water is controlled to be 2:3.

[0025] Optionally, in S6, during the coiling process of the hot-rolled steel strip, the coiling temperature of the hot-rolled steel strip is controlled to be 570°C-610°C.

[0026] It can be seen from the above technical scheme that the high corrosion-resistant low-alloy steel for photovoltaic brackets and the manufacturing method thereof provided by the present invention have the following advantages:

[0027] The high corrosion-resistant low alloy steel has low harmful and impurity elements, pure steel, high strength, and can reduce weight by 30% by replacing Q235B galvanized sheet, with significant lightweight effect. The high corrosion-resistant low alloy steel has strong corrosion resistance and can meet the requirements of photovoltaic brackets. At the same time, the high corrosion-resistant low alloy steel has excellent forming performance and can meet the demanding processing requirements of photovoltaic brackets.

[0028] At the same time, the P and Al contents in the high corrosion-resistant low alloy steel are moderate, and the Cu and Ti contents are low, which avoids their adverse effects on plasticity, toughness, welding performance, surface quality, etc., making the mechanical properties of the high corrosion-resistant low alloy steel more stable and easier to manufacture, thereby improving production efficiency.

[0029] In addition, the high corrosion-resistant low alloy steel does not contain precious alloy elements such as Ni, Nb, V, and Mo, and has a low Mn content, which effectively reduces the alloy cost. At the same time, the photovoltaic bracket made of the high corrosion-resistant low alloy steel does not require post-pickling, painting, and maintenance, and has the advantages of energy saving, environmental protection, short delivery cycle, and low cost of use.

[0030] Other features and advantages of the present invention will be set forth in the description which follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0032] Figure 1 The flowchart is a method for manufacturing high corrosion resistant low alloy steel in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] To make the purpose, technical solution and advantages of the present invention more clear, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other arbitrarily without conflict.

[0034] like Figure 1 The embodiment of the present invention is shown, in which a high corrosion-resistant low alloy steel for photovoltaic brackets is disclosed, and the composition of the high corrosion-resistant low alloy steel includes by mass percentage: C: 0.11%-0.13%, Si: 0.65%-0.79%, Mn: 0.31%-0.50%, P: 0.020%-0.030%, S: 0.0041%-0.0049%, Cr: 3.7%-3.9%, Cu: 0.13%-0.18%, Alt: 0.08%-0.12%, Sn≤0.015%, As≤0.025%, Sb≤0.015%, and the rest is Fe and unavoidable impurities. At the same time, the high corrosion-resistant low alloy steel satisfies Sn+As+Sb≤0.050%, (Sn+As+Sb) / Cu≤0.28.

[0035] The reasons for limiting the chemical elements in this embodiment are as follows:

[0036] It has been found in practice that an effective and economical way to improve the strength of steel is to increase the C content. However, as the C content increases, the plasticity, impact toughness, welding performance, forming performance, and corrosion resistance of the steel will decrease. In order to make the tensile strength of the steel strip in this embodiment reach more than 750MPa, and comprehensively consider the corrosion resistance, processing performance and welding performance, while taking into account the economy, the present invention controls the C content in the range of 0.11%-0.13%.

[0037] It has been found in practice that Si is not a precious alloy element, and its solid solution strengthening coefficient in ferrite is higher than that of Mn. Si is very effective in improving strength and corrosion resistance, but too high Si content reduces material toughness and is not conducive to improving welding performance. In order to make the tensile strength of the steel strip of the present invention reach more than 750MPa, and comprehensively consider corrosion resistance, processing performance and welding performance, while taking into account economy, the present invention controls the Si content in the range of 0.65%-0.79%.

[0038] It has been found in practice that Mn is an austenite forming element, which has the effect of stabilizing austenite, reducing the austenite transformation temperature, increasing the ferrite nucleation rate, and reducing the grain growth rate, that is, it has the effect of refining the grains. Mn can form a substitutional solid solution in steel, which plays a role in solid solution strengthening and increases the yield strength and tensile strength linearly. However, an increase in the Mn content can increase the C equivalent of the steel, which is not good for welding performance. In order to make the tensile strength of the steel strip of the present invention reach more than 750MPa, and comprehensively consider the processing performance and welding performance, while taking into account the economy, the present invention controls the Mn content in the range of 0.31%-0.50%.

[0039] It has been found in practice that the solid solution strengthening effect of P in steel is second only to C, and it can effectively improve the atmospheric corrosion resistance of steel. Among the many alloy elements that improve corrosion resistance, P is the most cost-effective element. However, P is easy to form and precipitate Fe3P in steel, which increases the brittleness of steel and is not conducive to improving the welding performance of steel. The diffusion rate of P in γ iron and α iron is low, and it is easy to form segregation, which has an adverse effect on the forming performance of steel. In order to make the tensile strength of the steel strip of the present invention reach more than 750MPa, and comprehensively consider the processing performance, welding performance and corrosion resistance, while taking into account the economy, the present invention controls the P content in the range of 0.020%-0.030%.

[0040] It has been found in practice that S is harmful to the corrosion resistance of steel, and the sulfides in steel can become the source of rust. A higher S content can cause "hot brittleness" defects in steel. Adding Mn and S to the steel to form MnS plastic inclusions can reduce the harmful effects of S. However, during the rolling process, the MnS extending along the rolling direction tends to form a banded structure in the steel strip, reducing the transverse impact toughness and forming properties of the steel strip, and causing anisotropy of mechanical properties. Therefore, the S content should be reduced as much as possible, but if the S content is controlled too low, the manufacturing cost will increase and the production efficiency will be reduced. Taking into account the corrosion resistance, uniformity of mechanical properties, and processing performance of the high corrosion-resistant steel strip of the present invention, while taking into account economy and production efficiency, the present invention controls the S content in the range of 0.0041%-0.0049%.

[0041] It has been found in practice that Cu is an effective element to improve the corrosion resistance of steel. It forms precipitates on the surface of steel and acts as a cathode to passivate the surface of steel. It is also enriched in the rust layer, changing the structure of the rust layer and preventing Cl - Invade the matrix. However, Cu has a low melting point (1083°C) and is easily segregated at the grain boundary during the heating process of the continuous casting billet. Too high a Cu content will cause a network crack defect during hot rolling. Cu is also a relatively expensive alloy element. Too high a Cu content will increase the product cost. Taking into account the corrosion resistance, hot working performance and surface quality of the high corrosion-resistant steel strip of the present invention, while taking into account the economy, the present invention controls the Cu content in the range of 0.13%-0.18%.

[0042] It has been found in practice that Cr can form a dense and uniform rust layer containing fine α-FeOOH on the surface of the substrate, accelerate the development of electrochemical corrosion products to a thermodynamically stable state, block the further penetration of corrosive media into the substrate, and reduce the corrosion rate of steel. Cr has a solid solution strengthening effect and can improve the hardenability and strength of steel. However, when the Cr content is too high, carbides will precipitate at the grain boundaries, reduce the plasticity and toughness of the steel, deteriorate the forming and welding properties, and increase the cost of the alloy. In order to make the tensile strength of the steel strip of the present invention reach more than 750MPa, and comprehensively consider the corrosion resistance, plasticity and toughness, processing properties, welding properties, and take into account economy, the present invention controls the Cr content in the range of 3.7%-3.9%.

[0043] It has been found in practice that the fine AlN formed by Al and N can inhibit the growth of austenite grains during the heating process of the continuous casting billet, has the effect of refining grains, and can improve the strength and toughness of steel and welding performance. Al has great potential in improving the corrosion resistance of steel and reducing costs. Under marine atmospheric conditions, Al and Si alloyed steel have a synergistic effect in improving the corrosion resistance of steel. The generated FeAl2O4 fine-grained spinel oxide can enhance the barrier effect of the rust layer on corrosive media and moisture. However, too high Al content will lead to the formation of more Al2O3 inclusions, which will reduce the purity of the steel and the impact performance, corrosion resistance and surface quality of the steel strip on the one hand, and on the other hand, it is very easy to block the water nozzle during continuous casting, increase the difficulty of production, reduce production efficiency, and increase the alloy cost and manufacturing cost. Taking into account the strength, welding performance, processing performance, impact performance, corrosion resistance and surface quality of the high corrosion-resistant steel strip of the present invention, and taking into account the difficulty of production, production efficiency and economy, the present invention controls the Alt content in the range of 0.08%-0.12%.

[0044] It has been found in practice that residual elements such as Sn, As, and Sb have low melting points. During the high-temperature cooling and reheating of the continuous casting billet, they will precipitate between the matrix and the iron scale and form a liquid-enriched phase, which will penetrate into the grain boundary and expand into a surface network crack during the subsequent rolling process. In order to avoid such defects, the content of individual elements Sn, As, and Sb and their total amount should be limited. With the increase of (Sn+As+Sb) / Cu, the melting point of Cu decreases, and the sensitivity of hot-rolled network crack defects caused by Cu segregation at the grain boundary is enhanced. Taking into account the corrosion resistance, processing performance and surface quality of the tensile strength high corrosion-resistant steel strip of the present invention, the present invention controls Sn≤0.015%, As≤0.025%, Sb≤0.015%, Sn+As+Sb≤0.050%, (Sn+As+Sb) / Cu≤0.28.

[0045] In this embodiment, the contents of the above-mentioned C, Si, Mn, P, S, Cu, Cr, Alt, Sn, As, and Sb elements and the selection of Sn+As+Sb have a synergistic effect. By controlling the content of each element and Sn+As+Sb within the above-mentioned range, the effects of solid solution strengthening, fine grain strengthening, and phase transformation strengthening can be fully exerted, so that the high corrosion-resistant low-alloy steel for photovoltaic brackets has high purity, high strength, and excellent cold processing properties.

[0046] Secondly, the selection of the above-mentioned Si, P, S, Cu, Cr, and Alt element contents has a synergistic effect. By controlling the content of each element within the above-mentioned range, a dense inner rust layer can be formed on the surface of the steel matrix, so that the high-corrosion-resistant low-alloy steel has high corrosion resistance, which can meet the service requirements of photovoltaic brackets. There is no need for subsequent pickling, painting and maintenance, which is energy-saving and environmentally friendly.

[0047] At the same time, the above-mentioned contents of C, Mn, S, Cu, Alt, Sn, As, and Sb elements and the selection of Sn+As+Sb, (Sn+As+Sb) / Cu have a synergistic effect. By controlling the content of each element and Sn+As+Sb, (Sn+As+Sb) / Cu within the above-mentioned range, defects such as hot-rolled network cracks can be avoided, and the high corrosion-resistant low-alloy steel for photovoltaic brackets has excellent hot processing properties and high surface quality, which can meet the stringent processing and service requirements of photovoltaic brackets.

[0048] Moreover, the contents of all the above-mentioned elements and the selection of Sn+As+Sb, (Sn+As+Sb) / Cu have a synergistic effect. By controlling the contents of all the elements and Sn+As+Sb, (Sn+As+Sb) / Cu within the above-mentioned ranges, the high corrosion-resistant low-alloy steel used for photovoltaic brackets has low processing difficulty, high production efficiency, low manufacturing cost and short delivery cycle.

[0049] The high corrosion resistant low alloy steel in this embodiment has at least the following properties:

[0050] (1) The yield strength of high corrosion resistant low alloy steel shall be ≥620MPa, the tensile strength shall be ≥750MPa, the elongation after fracture shall be ≥19%, and the 180°d=a cold bending test shall be qualified.

[0051] (2) After the high corrosion-resistant low alloy steel is periodically immersed in a mixed solution of NaHSO3 and 3.5% NaCl with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate is ≤30% relative to Q355B ordinary steel, and the corrosion rate is ≤50% relative to Q450NQR1 general weathering steel.

[0052] like Figure 1 As shown, this embodiment also discloses a method for manufacturing high corrosion-resistant low alloy steel for photovoltaic brackets, comprising the following steps:

[0053] S1, through hot metal pretreatment desulfurization, top and bottom composite blowing converter smelting, LF refining and slab continuous casting to obtain continuous casting billets;

[0054] S2, loading the continuous casting billet into a walking beam heating furnace for heating and heat preservation;

[0055] S3, rolling the continuous casting slab by a rough rolling mill to obtain a strip;

[0056] S4, rolling the strip with a finishing mill to obtain a hot-rolled steel strip;

[0057] S5, the hot rolled steel strip is cooled during transportation on a laminar cooling roller;

[0058] S6, coiling the hot-rolled steel strip into a hot-rolled steel coil by a coiler;

[0059] In S1, the composition of the continuous casting billet is controlled in percentage by mass: C: 0.11%-0.13%, Si: 0.65%-0.79%, Mn: 0.31%-0.50%, P: 0.020%-0.030%, S: 0.0041%-0.0049%, Cu: 0.13%-0.18%, Cr: 3.7%-3.9%, Alt: 0.08%-0.12%, Sn≤0.015%, As≤0.025%, Sb≤0.015%, and the rest are Fe and unavoidable impurities, and Sn+As+Sb≤0.050% and (Sn+As+Sb) / Cu≤0.28 in the continuous casting billet.

[0060] In S1, the thickness of the continuous casting billet is controlled to be 180-230 mm. It is found in practice that, under the premise of the width and length of the continuous casting billet being determined, the thicker the continuous casting billet is, the higher the output and yield rate are. However, the greater the mill load is, the greater the fluctuation of the final rolling temperature, microstructure and mechanical properties of the finished steel strip in the length direction is. The thickness of the continuous casting billet is also limited by the maximum outer diameter of the steel coil allowed by the coiler. Therefore, considering the above influences, the thickness of the continuous casting billet is controlled to be 180-230 mm in this embodiment.

[0061] In S2, the furnace discharge temperature of the continuous casting billet is controlled to be 1180℃-1200℃, and the cumulative furnace dwelling time is 180-210 minutes. It has been found in practice that if the furnace discharge temperature of the continuous casting billet is lower than 1180℃, the austenite grains can be refined, but the thermoplasticity of the continuous casting billet is poor, the deformation resistance is high, the thermal deformation is difficult, and the rolling mill operation rate is low. If the furnace discharge temperature of the continuous casting billet is higher than 1200℃, the austenite grains are easy to coarsen, but the thermoplasticity of the continuous casting billet is improved, the deformation resistance is reduced, it is easy to thermally deform, and the rolling mill operation rate is high. If the cumulative furnace dwelling time of the continuous casting billet is shorter than 180 minutes, its structure is not easy to be homogenized, the rolling energy consumption is high, and equipment accidents are prone to occur. If the cumulative furnace dwelling time of the continuous casting billet is longer than 210 minutes, oxidation burning, decarburization, energy consumption increase, and the rolling mill operation rate and production efficiency are reduced. Therefore, taking the above influences into comprehensive consideration, the present invention controls the holding temperature and the furnace-out temperature of the continuous casting billet to be 1180°C-1200°C.

[0062] In S3, the continuous casting billet is rough rolled by 7 rough rolling passes, and the rough rolling start temperature is controlled to be 1130℃-1150℃, the rough rolling final temperature is 1060℃-1100℃, the strip thickness is 28-40mm, and the absolute rough rolling reduction is shown in Table 1.

[0063] Table 1 Absolute reduction in rough rolling

[0064]

[0065] It has been found in practice that the main metallurgical purpose of rough rolling is to destroy the as-cast structure of the continuous casting billet, effectively refine the austenite grains through multiple recrystallizations, and obtain an austenite structure with uniform and fine grains. If the rough rolling start temperature is too high, uneven austenite grains will occur, resulting in differences in the strip structure and affecting the uniformity of the mechanical properties of the finished product. If the rough rolling start temperature is too low, the strip shape control becomes more difficult, the mill load and rolling energy consumption increase, and it is not conducive to smooth rolling. Therefore, taking the above influences into consideration, the present invention controls the rough rolling start temperature to 1130℃-1150℃, and the rough rolling final rolling temperature to 1060℃-1100℃.

[0066] It has been found in practice that if the strip is too thick, the cumulative reduction rate and pass reduction rate of rough rolling will decrease, partial recrystallization will easily occur, causing mixed crystal phenomenon, which will have an adverse effect on the uniformity of the mechanical properties of the finished steel strip. At the same time, it will increase the rolling load and rolling energy consumption of the finishing rolling unit, affecting the stability of finishing rolling.

[0067] If the strip is too thin, it is not conducive to improving the strip shape quality, and increases the rolling load and rolling energy consumption of the roughing mill, which is not conducive to smooth rolling. At the same time, it is impossible to ensure the finishing rolling start temperature required for rolling the 1.5-4.0mm thin finished steel strip of the present invention, and it is even possible to increase the rolling load and rolling energy consumption of the finishing mill. Therefore, considering the above influences, the present invention controls the strip thickness to be 28-40mm. According to the roughing mill power parameters, the continuous casting billet and the strip thickness, it can be calculated that the reasonable rolling pass of the roughing mill is 7 passes.

[0068] It has been found in practice that if the absolute reduction of the rough rolling mill is lower than the lower limit specified in Table 1, uneven grains will occur and plasticity will be reduced. If the absolute reduction is higher than the upper limit specified in Table 1, not only will the deformation resistance and load of the rough rolling mill increase, but buckling and warping will also occur. In severe cases, "roller wrapping" accidents may occur, leading to equipment hazards. Taking the above factors into consideration, the absolute reductions of the 7 rough rolling passes are determined to be 35.1-37.3mm, 32.1-34.3mm, 28.4-32.7mm, 28-30.9mm, 23.6-26.7mm, 21.7-25.3mm, and 21-24.2mm, respectively.

[0069] In S4, the strip is finish-rolled by a 7-stand finishing mill, and the finishing start temperature is controlled to be 1000°C-1050°C, the finishing final temperature is 850°C-890°C, the hot-rolled steel strip thickness is 1.5-4.0 mm, and the absolute reduction of finishing rolling is shown in Table 2.

[0070] Table 2 Absolute reduction of finishing rolling

[0071]

[0072] It has been found in practice that if the finishing rolling start temperature is too high, partial recrystallization will easily occur in the F1 and F2 finishing rolling stands, resulting in mixed crystal problems and differences in the structure of the finished steel strip and abnormal fluctuations in the mechanical properties. If the finishing rolling start temperature is too low, the desired final rolling temperature cannot be guaranteed. Therefore, considering the above factors comprehensively, the present invention controls the finishing rolling start temperature to 1000°C-1050°C.

[0073] It has been found in practice that if the finishing rolling temperature is too high, the finished steel strip will be coarsened and the toughness will be reduced. If the finishing rolling temperature is too low, the strength of the finished steel strip will be increased and the plasticity will be reduced, and the strength-plasticity matching will be unreasonable. At the same time, the rolling stability of the finishing rolling unit will be reduced, and the difficulty of controlling the thickness accuracy, width accuracy and cross-sectional shape of the steel strip will increase. In serious cases, the scrap steel strip will be rolled and the equipment will be damaged. Taking the above factors into consideration, the present invention controls the finishing rolling temperature to be 850℃-890℃.

[0074] It has been found in practice that the finishing rolling 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 selected by the user.

[0075] It has been found in practice that if the absolute reduction of each frame of the finishing mill is lower than the lower limit specified in Table 2, uneven grains will occur and plasticity will be reduced. If the absolute reduction is higher than the upper limit specified in Table 2, the deformation resistance and load of each frame of the finishing mill will increase, leading to equipment hazards. Taking the above factors into consideration, the absolute reduction of each frame of the finishing mill is determined to be 14.31-18.64mm, 5.75-8.95mm, 2.44-4.47mm, 1.28-2.46mm, 0.80-1.50mm, 0.36-0.90mm, and 0.17-0.64mm, respectively.

[0076] In S5, the cooling method of the hot-rolled steel strip on the laminar cooling roller is rear-stage cooling, and the flow ratio of the upper and lower header cooling water is controlled to be 2:3.

[0077] It has been found in practice that, compared with other cooling methods, the use of the back-end cooling method is conducive to the full precipitation of ferrite, the uniform size of ferrite grains, the reduced solid solution carbon content in ferrite crystals, and the increased density of movable dislocations, so that the strength, toughness, plasticity and cold forming properties of the finished steel strip are well matched. At the same time, the use of the back-end cooling method can make the hot-rolled steel strip run smoothly on the laminar cooling roller and coil smoothly, avoiding the occurrence of rolling accidents such as coiling and piling steel. Therefore, considering the above factors comprehensively, the cooling method of the hot-rolled steel strip on the laminar cooling roller of the present invention adopts the back-end cooling.

[0078] It has been found in practice that if the cooling water flow rate ratio of the upper and lower headers is higher or lower than 2:3, the cooling rates of the upper and lower surfaces of the steel strip will be greatly different, resulting in fluctuations in the organization and mechanical properties, and at the same time increasing the difficulty of plate shape control. Therefore, considering the above factors comprehensively, the present invention controls the cooling water flow rate ratio of the upper and lower headers to be 2:3.

[0079] In S6, during the hot-rolled steel strip coiling process, the hot-rolled steel strip coiling temperature is controlled to be 570°C-610°C.

[0080] It has been found in practice that by properly controlling the coiling temperature, the γ→α phase transformation temperature can be appropriately reduced, the α phase nucleation rate can be increased, the ferrite grains can be refined, and the proportion of bainite in the organization can be appropriately increased. The bainite grain size is finer than that of ferrite, about 1μm, and has a higher dislocation density, which can improve the comprehensive mechanical properties of the steel strip. In addition, the reasonable control of the coiling temperature is also a necessary measure to reduce the difficulty of controlling the plate shape and coil shape. Taking the above factors into consideration, the coiling temperature of the present invention is controlled to be 570℃-610℃.

[0081] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods without specific conditions in the following examples can be carried out according to conventional methods and conditions.

[0082] Embodiment 1-embodiment 3:

[0083] The chemical compositions, process parameters and properties of Examples 1 to 3 are shown in Tables 3 to 6.

[0084] Table 3 Chemical composition of the embodiments of the present invention (mass percentage)

[0085]

[0086] Table 4 Heating and rough rolling process parameters of the embodiment of the present invention

[0087]

[0088] Table 5 Finishing rolling and cooling process parameters of the embodiment of the present invention

[0089]

[0090] Table 6 Performance of the embodiment of the present invention

[0091]

[0092]

[0093] As shown in Tables 3 to 6, there are significant differences in the chemical composition, heating, rough rolling, fine rolling, cooling and other process parameters between the embodiments of the present invention and general weathering steel, and there are also significant differences in various performances. The high corrosion-resistant low-alloy steel in the present invention can better meet the new requirements for the development of photovoltaic brackets such as high strength, lightweight, high corrosion resistance, long life, easy manufacturing, low cost, high efficiency, painting-free, maintenance-free, energy saving, and environmental protection.

[0094] It can be seen from the above process that the high corrosion-resistant low-alloy steel and its manufacturing method in the present invention optimize the design of the content of elements such as C, Si, Mn, P, S, Cu, Cr, Alt, Sn, As, Sb, and control Sn+As+Sb, (Sn+As+Sb) / Cu, continuous casting billet discharge temperature and furnace residence time, rough rolling start and final rolling temperature, rolling pass, strip thickness, absolute reduction, finishing rolling start and final rolling temperature, rolling pass, finished product thickness, absolute reduction, cooling method, upper and lower header cooling water flow ratio and coiling temperature, so that the yield strength of the finished steel is ≥620MPa, the tensile strength is ≥750MPa, the elongation after fracture is ≥19%, and the 180°d=a cold bending test is qualified. At the same time, after 72 hours of periodic immersion in a mixed solution of NaHSO3 and 3.5% NaCl with an initial concentration of 0.01 mol / L, the corrosion rate of high corrosion-resistant low-alloy steel is ≤30% relative to Q355B ordinary steel, and ≤50% relative to Q450NQR1 general weathering steel.

[0095] The high corrosion-resistant low alloy steel in the present invention has low harmful and impurity element content, pure steel quality, high strength, and can reduce weight by 30% by replacing Q235B galvanized sheet, with significant lightweight effect. The high corrosion-resistant low alloy steel has strong corrosion resistance and can meet the service requirements of photovoltaic brackets. At the same time, the high corrosion-resistant low alloy steel has excellent forming performance and can meet the demanding processing requirements of photovoltaic brackets.

[0096] At the same time, the P and Al contents in the high corrosion-resistant low alloy steel are moderate, and the Cu and Ti contents are low, which avoids their adverse effects on plasticity, toughness, welding performance, surface quality, etc., making the mechanical properties of the high corrosion-resistant low alloy steel more stable and easier to manufacture, thereby improving production efficiency.

[0097] In addition, the high corrosion-resistant low alloy steel does not contain precious alloy elements such as Ni, Nb, V, and Mo, and has a low Mn content, which effectively reduces the production cost of the alloy. At the same time, the photovoltaic bracket made of the high corrosion-resistant low alloy steel does not require subsequent pickling, painting, and maintenance, and has the advantages of energy saving, environmental protection, short delivery cycle, and low cost of use.

[0098] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in the present invention should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0099] In addition, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. In the description of the present invention, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A high corrosion resistant low alloy steel for photovoltaic support, characterized in that: The composition of the high corrosion resistant low alloy steel includes, by mass percentage: C: 0.11%-0.13%, Si: 0.65%-0.79%, Mn: 0.31%-0.50%, P: 0.020%-0.030%, S: 0.0041%-0.0049%, Cr: 3.7%-3.9%, Cu: 0.13%-0.18%, Alt: 0.08%-0.12%, Sn≤0.015%, As≤0.025%, Sb≤0.015%, and the rest is Fe and unavoidable impurities; The high corrosion resistant low alloy steel satisfies Sn+As+Sb≤0.050%, (Sn+As+Sb) / Cu≤0.

28.

2. The high corrosion resistant low alloy steel according to claim 1, characterized in that: The high corrosion resistant low alloy steel has the following properties: Yield strength ≥620MPa, tensile strength ≥750MPa, elongation after fracture ≥19%, 180°d=a cold bending test qualified; After 72 hours of periodic immersion in a mixed solution of NaHSO3 and 3.5% NaCl with an initial concentration of 0.01 mol / L, the corrosion rate is ≤30% relative to Q355B ordinary steel, and the corrosion rate is ≤50% relative to Q450NQR1 general weathering steel.

3. A method for manufacturing high corrosion resistant low alloy steel according to claim 1 or 2, characterized in that: The steps include: S1, through hot metal pretreatment desulfurization, top and bottom composite blowing converter smelting, LF refining and slab continuous casting, to obtain a continuous casting billet with a thickness of 180-230mm; S2, loading the continuous casting billet into a walking beam heating furnace for heating and heat preservation; S3, rolling the continuous casting slab by a rough rolling mill to obtain a strip; S4, rolling the strip by a finishing mill to obtain a hot-rolled steel strip; S5, the hot-rolled steel strip is cooled during transportation on a laminar cooling roller; S6, coiling the hot-rolled steel strip into a hot-rolled steel coil by a coiler.

4. The method for producing high corrosion resistant low alloy steel according to claim 3, characterized in that: In S2, the temperature of the continuous casting billet out of the furnace is controlled to be 1180°C-1200°C, and the cumulative residence time in the furnace is 180-210 minutes.

5. The method for manufacturing high corrosion resistant low alloy steel according to claim 3, characterized in that: In S3, the continuous casting billet is rough rolled through 7 rough rolling passes, and the rough rolling start temperature is controlled to be 1130°C-1150°C, the rough rolling finish temperature is controlled to be 1060°C-1100°C, and the strip thickness is controlled to be 28-40mm.

6. The method for producing high corrosion resistant low alloy steel according to claim 5, characterized in that: In S3, the absolute reduction of each rough rolling pass is: 35.1-37.3mm, 32.1-34.3mm, 28.4-32.7mm, 28-30.9mm, 23.6-26.7mm, 21.7-25.3mm, and 21-24.2mm.

7. The method for producing high corrosion resistant low alloy steel according to claim 3, characterized in that: In S4, the strip is finish-rolled by a 7-stand finishing mill, and the finishing rolling start temperature is controlled to be 1000°C-1050°C, the finishing rolling final temperature is 850°C-890°C, and the thickness of the hot-rolled steel strip is 1.5-4.0 mm.

8. The method for producing high corrosion resistant low alloy steel according to claim 7, characterized in that: In S4, the absolute reduction of each finishing rolling stand is: 14.31-18.64mm, 5.57-8.95mm, 2.44-4.47mm, 1.28-2.46mm, 0.80-1.5mm, 0.36-0.9mm, and 0.17-0.64mm.

9. The method for producing high corrosion resistant low alloy steel according to claim 3, characterized in that: In S5, the cooling method of the hot-rolled steel strip on the laminar cooling roller is rear-stage cooling, and the flow ratio of the upper and lower header cooling water is controlled to be 2:

3.

10. The method for producing high corrosion resistant low alloy steel according to claim 3, characterized in that: In S6, during the hot-rolled steel strip coiling process, the hot-rolled steel strip coiling temperature is controlled to be 570°C-610°C.

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