Steel coil for photovoltaic bracket and preparation method of steel coil

Abstract

The invention relates to a steel coil for a photovoltaic support and a preparation method of the steel coil. The preparation method comprises the steps that a continuous casting blank is obtained; rolling the continuous casting billet to obtain a hot rolled steel strip; coiling the steel strip into a steel coil; the continuous casting billet is prepared from the following components in percentage by mass: 0.02 percent to 0.04 percent of C, 0.76 percent to 0.85 percent of Si, 0.71 percent to 0.80 percent of Mn, 0.076 percent to 0.085 percent of P, 0.0071 percent to 0.0080 percent of S, 0.13 percent to 0.18 percent of Cu, 2.2 percent to 2.4 percent of Cr, 0.046 percent to 0.055 percent of Ti, 0.23 percent to 0.27 percent of Als, 0.25 percent to 0.28 percent of Alt and the balance of Fe and inevitable impurities. The steel coil prepared by the invention can better meet the new development requirements of the photovoltaic bracket.

Description

Technical Field

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

[0002] Photovoltaic power generation has the characteristics of being noise-free, pollution-free, and easy to maintain. It is a green and environmentally friendly industry with broad development space and application prospects.

[0003] Photovoltaic bracket is an important supporting and protective structure of photovoltaic power generation device. In order to prevent the corrosion of photovoltaic bracket, most of them are galvanized by Q235 and Q355 material coils, but the production of hot-dip galvanized products will pollute the environment.

[0004] Weathering steel is an ideal product for manufacturing photovoltaic brackets. In order to improve strength and corrosion resistance, high content of precious alloy elements such as V, Nb, Ni, and Cu are generally added when producing weathering steel for photovoltaic brackets in China, which increases production costs. In addition, the plasticity is insufficient and cannot meet the stringent processing requirements of photovoltaic brackets. The research and development of high-strength, high-corrosion-resistant, high-plasticity, low-cost weathering steel for photovoltaic brackets is of great significance.

[0005] So far, no relevant reports have been found on low-alloy corrosion-resistant steel with high plasticity for photovoltaic brackets and its manufacturing method. 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 steel coil for photovoltaic brackets and a preparation method thereof. The difficulty of producing hot-rolled steel coils using the preparation method of the present invention is small; the obtained steel coil has high plasticity, high strength, good forming and welding properties, and excellent corrosion resistance.

[0007] According to one aspect of the present invention, there is provided a method for preparing a steel coil for a photovoltaic support, comprising:

[0008] Obtaining a continuous casting billet through pretreatment;

[0009] Heating and heat-insulating the continuous casting billet;

[0010] Rough rolling the continuous casting billet using a rough rolling mill to obtain a strip billet;

[0011] Using a finishing mill to finish-roll the strip to obtain a hot-rolled steel strip; and

[0012] Cooling the hot-rolled steel strip, and coiling the cooled hot-rolled steel strip into a steel coil;

[0013] Wherein, the continuous casting billet comprises the following components by mass percentage:

[0014] C: 0.02%-0.04%, Si: 0.76%-0.85%, Mn: 0.71%-0.80%, P: 0.076%-0.085%, S: 0.0071%-0.0080%, Cu: 0.13%-0.18%, Cr: 2.2%-2.4%, Ti: 0.046%-0.055%, Als: 0.23%-0.27%, Alt: 0.25%-0.28%, and the rest are Fe and unavoidable impurities.

[0015] Furthermore, the continuous casting billet also needs to satisfy Als / Alt≥0.95.

[0016] Furthermore, the method of obtaining the continuous casting billet by pretreatment specifically comprises: obtaining the continuous casting billet by desulfurization of molten iron pretreatment, top and bottom composite blowing converter smelting, LF refining and slab continuous casting; the thickness of the continuous casting billet is 180-230 mm.

[0017] Furthermore, the heating and heat preservation treatment of the continuous casting billet further comprises: loading the continuous casting billet into a walking beam heating furnace; and heating and heat preservation treatment of the continuous casting billet in the walking beam heating furnace;

[0018] The furnace discharge temperature of the continuous casting billet is 1210-1230° C., and the cumulative furnace residence time of the continuous casting billet is 180-210 minutes.

[0019] Further, the step of rough rolling the continuous casting billet with a rough rolling mill to obtain a strip billet is as follows: the starting rolling temperature of the rough rolling is controlled to be 1160-1180° C., the final rolling temperature of the rough rolling is controlled to be 1090-1120° C., and the continuous casting billet is rolled with a rough rolling mill to obtain a strip billet;

[0020] The thickness of the strip obtained by rough rolling is 28-40 mm, and the number of rough rolling passes is 7.

[0021] Further, the use of a finishing mill to finish-roll the strip to obtain a hot-rolled steel strip is specifically as follows: the start rolling temperature of the finishing rolling is controlled to be 1060-1110° C., the final rolling temperature of the finishing rolling is controlled to be 880-920° C., and the finishing mill is used to finish-roll the strip to obtain a hot-rolled steel strip;

[0022] Among them, the thickness of the hot-rolled steel strip obtained by finish rolling is 1.5-4.0 mm. The finish rolling adopts a 7-stand finishing rolling unit, and the rolling temperature of each stand is: 1028-1068°C for the first stand, 999-1039°C for the second stand, 977-1015°C for the third stand, 951-991°C for the fourth stand, 935-973°C for the fifth stand, 916-958°C for the sixth stand, and 892-942°C for the seventh stand.

[0023] Furthermore, the step of cooling the hot-rolled steel strip and coiling the cooled hot-rolled steel strip into a steel coil specifically comprises:

[0024] The hot-rolled steel strip transported on the laminar cooling roller is cooled, wherein the cooling method of the hot-rolled steel strip on the laminar cooling roller is rear-stage sparse cooling, and the upper and lower header cooling water flow ratio during the cooling process is 4:6; and the coiling temperature is controlled to be 500-540°C, and the cooled hot-rolled steel strip is coiled into a steel coil by a coiler.

[0025] The present invention also provides a steel coil for a photovoltaic support, which is prepared by any one of the preparation methods described above.

[0026] Furthermore, the microstructure of the steel coil is ferrite and bainite, wherein the ferrite ratio is 66-76% and the bainite ratio is 24-34%;

[0027] The steel coil has a yield strength of ≥420MPa, a tensile strength of ≥550MPa, an elongation after fracture of ≥28%, and passes a 180°d=0 cold bending test;

[0028] After the steel coil is periodically immersed in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate of the steel coil is ≤28% relative to that of Q355B ordinary steel.

[0029] It can be seen from the above technical solution that the photovoltaic support steel coil and the preparation method thereof provided by the present invention have the following beneficial effects:

[0030] The steel coil prepared by the preparation method of the present invention can better meet the new requirements for the development of photovoltaic brackets such as high strength, light weight, high corrosion resistance, long life, high plasticity, easy manufacturing, low cost, high efficiency, painting-free, maintenance-free, energy-saving, and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, serve to explain the principles of the present invention.

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0033] Figure 1 A flow chart of a preparation method according to an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of a cold bending test performed on a steel coil sample according to an embodiment of the present invention, showing the sample after the test. DETAILED DESCRIPTION

[0035] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0036] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0037] A method for preparing a steel coil for a photovoltaic support according to an embodiment of the present invention, such as Figure 1 As shown, including:

[0038] Step S001: obtaining a continuous casting billet through pretreatment;

[0039] Step S002: heating and heat-insulating the continuous casting billet;

[0040] Step S003: rough rolling the continuous casting billet using a rough rolling mill to obtain a strip billet;

[0041] Step S004: using a finishing mill to finish-roll the strip to obtain a hot-rolled steel strip; and

[0042] Step S005: cooling the hot-rolled steel strip, and coiling the cooled hot-rolled steel strip into a steel coil;

[0043] Wherein, the continuous casting billet in step S001 includes the following components by mass percentage:

[0044] C: 0.02%-0.04%, Si: 0.76%-0.85%, Mn: 0.71%-0.80%, P: 0.076%-0.085%, S: 0.0071%-0.0080%, Cu: 0.13%-0.18%, Cr: 2.2%-2.4%, Ti: 0.046%-0.055%, Als: 0.23%-0.27%, Alt: 0.25%-0.28%, and the rest are Fe and unavoidable impurities.

[0045] The steel coil prepared by the preparation method of the embodiment of the present invention has a tensile strength of more than 550 MPa and has high plasticity.

[0046] The reasons for limiting the chemical elements in the embodiments of the present invention are as follows:

[0047] It has been found in practice that increasing the C content is an effective and economical method to increase the strength of steel. 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 of the embodiment of the present invention reach more than 550MPa, and comprehensively consider the processing performance, welding performance and corrosion resistance, while taking into account the economy, the C content of the embodiment of the present invention is controlled in the range of 0.02%-0.04%.

[0048] Si is not a precious alloy element. It has been found in practice that its solid solution strengthening coefficient in ferrite is higher than that of Mn. Si is very effective in improving strength and corrosion resistance. However, too high Si content will reduce material toughness and is not conducive to improving welding performance. In order to make the tensile strength of the steel strip of the embodiment of the present invention reach more than 550MPa, and comprehensively consider plasticity, processing performance, welding performance and corrosion resistance, while taking into account economy, the present invention controls the Si content in the range of 0.76%-0.85%.

[0049] It has been found in practice that 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. Mn is an austenite-forming element, which has the function of stabilizing austenite, can reduce the austenite transformation temperature (Ar3), increase the ferrite nucleation rate, and reduce the grain growth rate, that is, it has the function of refining the grains. However, an increase in the Mn content can increase the C equivalent (Ceq) of the steel, which is not good for welding performance. In order to make the tensile strength of the steel strip of the embodiment of the present invention reach more than 550MPa, and comprehensively consider the plasticity, processing performance, welding performance, and economic efficiency, the embodiment of the present invention controls the Mn content in the range of 0.71%-0.80%.

[0050] 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 embodiment of the present invention reach more than 550MPa, and comprehensively consider the plasticity, processing performance, welding performance and corrosion resistance, while taking into account economy, the embodiment of the present invention controls the P content in the range of 0.076%-0.085%.

[0051] It has been found in practice that 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, which reduces the transverse impact toughness and forming properties of the steel strip, and leads to anisotropy of mechanical properties. S is harmful to the corrosion resistance of steel, and the sulfides in the steel can become the source of rust. 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 uniformity of mechanical properties, processing properties and corrosion resistance of the high-plasticity steel strip in the embodiment of the present invention, while taking into account economy and production efficiency, the S content in the embodiment of the present invention is controlled in the range of 0.0071%-0.0080%.

[0052] It has been found in practice that Cu forms precipitates on the surface of steel and acts as a cathode to passivate the surface of the steel and accumulate in the rust layer, changing the structure of the rust layer and preventing Cl - Invades the matrix, so Cu is an effective element to improve the corrosion resistance of steel. 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 precious alloying element, and too high a Cu content will lead to an increase in product cost. Taking into account the hot working performance, surface quality and corrosion resistance of the high-plasticity steel strip in the embodiment of the present invention, while taking into account the economy, the embodiment of the present invention controls the Cu content in the range of 0.13%-0.18%.

[0053] It has been found in practice that Cr has a solid solution strengthening effect, which can improve the hardenability and strength of steel, 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. 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 alloy cost. In order to make the tensile strength of the steel strip of the embodiment of the present invention reach more than 550MPa, and comprehensively consider the corrosion resistance, plasticity and toughness, processing properties, welding properties, and take into account economy, the embodiment of the present invention controls the Cr content in the range of 2.2%-2.4%.

[0054] It has been found in practice that TiN formed by Ti and N can inhibit the growth of austenite grains during the heating process of the continuous casting billet, which is beneficial to improving the strength and toughness and welding performance of the steel. Ti and C form nano-scale TiC precipitates during the hot rolling process, which have fine grain strengthening and precipitation strengthening effects, and can improve the strength and toughness of the steel. If the Ti content is high, on the one hand, coarse TiN precipitates are easily formed, and become stress concentration points and microcrack sources, reducing the forming and fatigue performance of the photovoltaic bracket. On the other hand, the recovery rate of Ti is unstable and the mechanical properties fluctuate greatly. Therefore, a large Ti content will increase the difficulty of photovoltaic bracket processing and reduce processing efficiency. Taking into account the strength and toughness, welding performance, processing performance and use performance of the high-plasticity steel strip in the embodiment of the present invention, the embodiment of the present invention controls the Ti content in the range of 0.046%-0.055%.

[0055] 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 and welding performance of steel. In the marine atmosphere environment, Al and Si have a synergistic effect, so that the generated rust layer has a strong barrier effect against corrosive media and moisture. However, too high an 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 and toughness, welding performance, processing performance, impact performance, corrosion resistance and surface quality of the high-plasticity steel strip in the embodiment of the present invention, and taking into account the difficulty of production, production efficiency and economy, the embodiment of the present invention controls the Als content in the range of 0.23%-0.27%, and controls the Alt content in the range of 0.25%-0.28%.

[0056] Among them, the continuous casting billet in step S001 also needs to satisfy Als / Alt≥0.95. It has been found in practice that the higher the Als / Alt ratio, the more significant the beneficial effect of Al in refining grains and improving the strength and toughness of steel, so Als / Alt should be increased as much as possible. According to experience, the embodiment of the present invention controls Als / Alt≥0.95.

[0057] The selection of the above-mentioned C, Si, Mn, P, S, Cu, Cr, Ti, Als, Alt and Als / Alt has a synergistic effect. By controlling the content of each element within the above-mentioned range, the solid solution strengthening, fine grain strengthening and phase transformation strengthening effects can be fully exerted, so that the high plasticity low alloy corrosion-resistant steel for photovoltaic brackets has high purity, high strength and excellent cold processing performance.

[0058] The selection of the above-mentioned Si, P, S, Cu, Cr, Als 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-plasticity low-alloy corrosion-resistant steel for photovoltaic brackets has high corrosion resistance, which can meet the processing and service requirements of photovoltaic brackets, and does not require subsequent pickling, painting and maintenance, and has the advantages of energy saving and environmental protection.

[0059] The selection of the above-mentioned C, Mn, S, Cu, Als and Alt has a synergistic effect. By controlling the content of each element within the above-mentioned range, defects such as hot-rolled network cracks can be avoided, so that the high-plasticity low-alloy corrosion-resistant steel for photovoltaic brackets has excellent hot processing properties and high surface quality, which can meet the demanding processing and service requirements of photovoltaic brackets.

[0060] The content of all the above elements and the selection of Als / Alt have a synergistic effect. By controlling the content of all the elements and Als / Alt within the above range, the high-plasticity, low-alloy, corrosion-resistant steel for photovoltaic brackets has low processing difficulty, high production efficiency, low manufacturing cost and short delivery cycle.

[0061] Among them, step S001 obtains the continuous casting billet through pretreatment, specifically: obtains the continuous casting billet through molten iron pretreatment desulfurization, top and bottom composite blowing converter smelting, LF refining and slab continuous casting; the thickness of the continuous casting billet is 180-230mm.

[0062] It has been found in practice that, under the premise of determining the width and length of the continuous casting billet, the thicker the continuous casting billet, the higher the output and yield rate, but the greater the mill load, the greater the fluctuation of the final rolling temperature, microstructure and mechanical properties of the finished steel strip in the length direction, and the thickness of the continuous casting billet is also limited by the maximum outer diameter of the steel coil allowed by the coiler. Taking the above influences into consideration, the embodiment of the present invention controls the thickness of the continuous casting billet to be 180-230mm.

[0063] Wherein, step S002 of heating and heat-insulating the continuous casting billet further comprises: loading the continuous casting billet into a walking beam heating furnace; and heating and heat-insulating the continuous casting billet in the walking beam heating furnace;

[0064] The furnace discharge temperature of the continuous casting billet is 1210-1230°C, and the cumulative furnace residence time of the continuous casting billet is 180-210 minutes.

[0065] It has been found in practice that if the furnace discharge temperature of the continuous casting billet is lower than 1210°C, the austenite grains can be refined, but the thermoplasticity of the continuous casting billet is poor, the deformation resistance is high, and thermal deformation is difficult, which will lead to a low subsequent rolling mill operating rate; if the furnace discharge temperature of the continuous casting billet is higher than 1230°C, although the thermoplasticity of the continuous casting billet is improved, the deformation resistance is reduced, and it is easy to be thermally deformed, the corresponding subsequent rolling mill operating rate will be improved, but the austenite grains are easy to coarsen. Taking the above influences into consideration, the embodiment of the present invention controls the furnace discharge temperature of the continuous casting billet to be 1210-1230°C. If the cumulative furnace residence 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 residence time of the continuous casting billet is longer than 210 minutes, it is easy to be oxidized, burned and decarburized, which will increase energy consumption accordingly, and the rolling mill operating rate and production efficiency will be reduced. Taking the above influences into consideration, the embodiment of the present invention controls the furnace discharge temperature of the continuous casting billet to 1210-1230° C., and the cumulative furnace residence time to 180-210 minutes.

[0066] Among them, step S003 uses a rough rolling mill to rough roll the continuous casting billet to obtain a strip billet. Specifically, the starting rolling temperature of the rough rolling is controlled to be 1160-1180°C, the final rolling temperature of the rough rolling is controlled to be 1090-1120°C, and the continuous casting billet is rolled by the rough rolling mill to obtain a strip billet.

[0067] 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. Taking the above influences into consideration, the embodiment of the present invention controls the rough rolling start temperature to 1160-1180°C, and the rough rolling final rolling temperature to 1090-1120°C.

[0068] The thickness of the strip obtained by rough rolling is 28-40 mm, and the number of rough rolling passes is 7.

[0069] 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 be reduced, partial recrystallization is prone to occur, causing mixed crystal phenomenon, and having 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 mill, affecting the stability of finishing rolling. If the strip is too thin, it is not conducive to improving the quality of the strip shape, and increases the rolling load and rolling energy consumption of the roughing mill, which is not conducive to the smooth rolling. At the same time, it cannot guarantee the finishing rolling start temperature required for rolling the 1.5-4.0mm thin finished steel strip of the present invention, and may even increase the rolling load and rolling energy consumption of the finishing mill. Taking the above influences into consideration, the embodiment of the present invention controls the strip thickness to be 28-40mm. According to the roughing mill force and energy 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.

[0070] Among them, step S004 uses a finishing mill to finish rolling the strip to obtain a hot-rolled steel strip. Specifically, the starting rolling temperature of the finishing rolling is controlled to be 1060-1110°C, the final rolling temperature of the finishing rolling is controlled to be 880-920°C, and the finishing mill is used to finish rolling the strip to obtain a hot-rolled steel strip.

[0071] It has been found in practice that if the finishing rolling start temperature is too high, partial recrystallization will easily occur in the first stand (F1) and the second stand (F2), resulting in mixed crystal problems and differences in the finished steel strip structure and abnormal fluctuations in mechanical properties; if the finishing rolling start temperature is too low, the desired final rolling temperature cannot be guaranteed. Taking the above factors into consideration, the finishing rolling start temperature is controlled to be 1060-1110°C in the embodiment of the present invention.

[0072] 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 finishing rolling temperature of the embodiment of the present invention is controlled to be 880-920℃.

[0073] Among them, the thickness of the hot rolled steel strip obtained by the finish rolling is 1.5-4.0 mm. The finish rolling adopts a 7-stand finishing rolling unit. The rolling temperatures of each stand are: the first stand (F1) 1028-1068°C, the second stand (F2) 999-1039°C, the third stand (F3) 977-1015°C, the fourth stand (F4) 951-991°C, the fifth stand (F5) 935-973°C, the sixth stand (F6) 916-958°C, and the seventh stand (F7) 892-942°C, see Table 1.

[0074] Table 1 Finishing process of steel coil for photovoltaic support (finishing rolling temperature of each rack)

[0075] Rack number F1 F2 F3 F4 F5 F6 F7 Finishing rolling temperature(℃) 1028-1068 999-1039 977-1015 951-991 935-973 916-958 892-942

[0076] Among them, the finishing rolling adopts a 7-stand finishing rolling unit which 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.

[0077] It has been found in practice that if the finishing temperature is too high, partial recrystallization will easily occur in the front frame, leading to mixed crystal problems, differences in the structure of the finished steel strip, and abnormal fluctuations in mechanical properties; if the finishing temperature is too low, the strength and plasticity matching of the finished steel strip will be unreasonable, and the rolling stability of the finishing mill will decrease, making it more difficult to control the thickness accuracy, width accuracy and cross-sectional shape of the steel strip. In severe cases, scrap steel strips will be rolled and equipment will be damaged. Taking the above factors into consideration, the finishing temperature of the embodiment of the present invention is controlled as shown in Table 1.

[0078] Among them, step S005 cools the hot-rolled steel strip and coils the cooled hot-rolled steel strip into a steel coil. Specifically, the hot-rolled steel strip transported on the laminar cooling roller is cooled, wherein the cooling method of the hot-rolled steel strip on the laminar cooling roller is rear-stage sparse cooling, and the upper and lower header cooling water flow ratio during the cooling process is 4:6; and the coiling temperature is controlled to be 500-540°C, and the cooled hot-rolled steel strip is coiled into a steel coil by a coiler.

[0079] It has been found in practice that compared with other cooling methods, the use of the latter sparse cooling method is conducive to the full precipitation of ferrite, uniform ferrite grain size, reduced solid solution carbon content in ferrite crystals, and increased movable dislocation density, thereby making the strength, toughness, plasticity and cold forming properties of the finished steel strip well matched.

[0080] In addition, the use of the rear-stage sparse cooling method can make the 1.5-4.0 mm thin finished steel strip of the embodiment of the present invention run smoothly on the laminar cooling roller and be coiled smoothly, avoiding rolling accidents such as coiling and steel piling. Taking the above factors into consideration, the cooling method of the hot-rolled steel strip on the laminar cooling roller of the embodiment of the present invention is the rear-stage sparse cooling.

[0081] It has been found in practice that if the cooling water flow ratio of the upper and lower headers is higher or lower than 4:6, the cooling rates of the upper and lower surfaces of the steel strip will be greatly different, resulting in fluctuations in the microstructure and mechanical properties, and increasing the difficulty of plate shape control. Taking the above factors into consideration, the embodiment of the present invention controls the cooling water flow ratio of the upper and lower headers to be 4:6.

[0082] 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, and the ferrite grains can be refined. At the same time, the proportion of bainite in the structure is 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, 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 in the embodiment of the present invention is controlled to be 500-540℃.

[0083] 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 are based on conventional methods and conditions.

[0084] Embodiment 1-embodiment 3:

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

[0086] First, a continuous casting billet is obtained by pre-treatment of molten iron for desulfurization, top and bottom composite blowing in converter smelting, LF refining and slab continuous casting. The chemical compositions of the continuous casting billets obtained in Examples 1 to 3 are shown in Table 2.

[0087] Table 2 Chemical composition (mass percentage) of the continuous casting slabs of Examples 1 to 3 of the present invention

[0088] C Si Mn P S Cr Cu Ti Als Alt Als / Alt (ratio) Example 1 0.036 0.81 0.75 0.083 0.0073 2.35 0.15 0.054 0.260 0.268 0.97 Example 2 0.035 0.83 0.74 0.078 0.0076 2.24 0.16 0.048 0.241 0.253 0.95 Example 3 0.026 0.78 0.78 0.082 0.0078 2.26 0.18 0.052 0.261 0.271 0.96

[0089] Secondly, the continuous casting billet is heated, rough rolled, finished rolled, and cooled to obtain a hot-rolled steel strip, which is then coiled to obtain a hot-rolled steel coil. The process parameters of each process are shown in Table 3-Table 4, and the properties of the obtained steel coil are shown in Table 5.

[0090] Table 3 Heating and rough rolling process parameters of Examples 1 to 3 of the present invention

[0091]

[0092] Table 4 Process parameters of finishing rolling, cooling and coiling of Examples 1 to 3 of the present invention

[0093]

[0094] Table 5 Performance of steel coils obtained from Examples 1 to 3 of the present invention

[0095]

[0096] As can be seen from Tables 2-5, there are significant differences in the chemical composition, heating, rough rolling, finishing rolling, cooling and other process parameters between Examples 1-3 of the present invention and general weathering steel, and there are also significant differences in microstructure and various properties. The steel coils prepared by the embodiments of the present invention can better meet the new requirements for the development of photovoltaic brackets such as high strength, light weight, high corrosion resistance, long life, high plasticity, easy manufacturing, low cost, high efficiency, free painting, maintenance-free, energy saving, and environmental protection.

[0097] The preparation method of the embodiment of the present invention optimizes the content of elements such as C, Si, Mn, P, S, Cu, Cr, Ti, Als, Alt, etc., and controls Als / Alt, continuous casting billet discharge temperature, furnace residence time, rough rolling start and final rolling temperature, rolling pass, strip thickness, finishing rolling start and final rolling temperature, rolling pass, finished product thickness, rolling temperature, cooling method, upper and lower header cooling water flow ratio, coiling temperature, so that the microstructure of the obtained finished steel is composed of 66-76% ferrite and 24-34% bainite; and the yield strength of the obtained steel coil is ≥420MPa, the tensile strength is ≥550MPa, and the elongation after fracture is ≥28%; such as Figure 2 As shown, the steel coil sample of the embodiment of the present invention passed the 180° d=0 cold bending test; after periodic immersion in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate relative to Q355B ordinary steel was ≤28%.

[0098] The steel coil prepared by the preparation method of the embodiment of the present invention has low content of harmful and impurity elements, pure steel, high strength, and can reduce weight by 20% by replacing Q235B galvanized sheet, with a significant lightweight effect. It has strong corrosion resistance and can meet the requirements of photovoltaic brackets for painting-free service. It has excellent forming performance and can meet the demanding processing requirements of photovoltaic brackets. The P and Al contents are moderate, and the Cu and Ti contents are low, which avoids their adverse effects on plastic toughness, welding performance, surface quality, etc., and has stable mechanical properties, low manufacturing difficulty and high production efficiency. It does not contain precious alloy elements such as Ni, Nb, V, Mo, etc., has a low Mn content, and has a low alloy cost. No need for post-pickling, painting and maintenance, energy saving, environmental protection, short delivery cycle and low cost of use.

[0099] The steel coil prepared by the preparation method of the embodiment of the present invention can better meet the new requirements for the development of photovoltaic brackets such as high strength, light weight, high corrosion resistance, long life, high plasticity, easy manufacturing, low cost, high efficiency, painting-free, maintenance-free, energy-saving, and environmental protection.

[0100] An embodiment of the present invention further provides a steel coil for a photovoltaic support, which is prepared by the preparation method of any one of the above embodiments.

[0101] The microstructure of the steel coil is ferrite and bainite, wherein the proportion of ferrite is 66-76% and the proportion of bainite is 24-34%.

[0102] The yield strength of the steel coil is ≥420MPa, the tensile strength is ≥550MPa, the elongation after fracture is ≥28%, and the 180°d=0 cold bending test is qualified.

[0103] After the steel coil was periodically immersed in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate was ≤28% relative to that of Q355B ordinary steel.

[0104] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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. 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 method for preparing a steel coil for a photovoltaic support, characterized in that: include: Obtaining a continuous casting billet through pretreatment; Heating and heat-insulating the continuous casting billet; Rough rolling the continuous casting billet using a rough rolling mill to obtain a strip billet; The strip is finish-rolled by a finishing mill to obtain a hot-rolled steel strip; as well as Cooling the hot-rolled steel strip, and coiling the cooled hot-rolled steel strip into a steel coil; Wherein, the continuous casting billet comprises the following components by mass percentage: C: 0.02%-0.04%, Si: 0.76%-0.85%, Mn: 0.71%-0.80%, P: 0.076%-0.085%, S: 0.0071%-0.0080%, Cu: 0.13%-0.18%, Cr: 2.2%-2.4%, Ti: 0.046%-0.055%, Als: 0.23%-0.27%, Alt: 0.25%-0.28%, and the rest are Fe and unavoidable impurities.

2. The preparation method according to claim 1, characterized in that: The continuous casting billet also needs to satisfy Als / Alt≥0.

95.

3. The preparation method according to claim 1, characterized in that: The continuous casting billet obtained by pretreatment specifically comprises: obtaining the continuous casting billet through molten iron pretreatment desulfurization, top and bottom composite blowing converter smelting, LF refining and slab continuous casting; the thickness of the continuous casting billet is 180-230 mm.

4. The preparation method according to claim 1, characterized in that: The heating and heat preservation treatment of the continuous casting billet further comprises: loading the continuous casting billet into a walking beam heating furnace; and heating and heat preservation treatment of the continuous casting billet in the walking beam heating furnace; The furnace discharge temperature of the continuous casting billet is 1210-1230° C., and the cumulative furnace residence time of the continuous casting billet is 180-210 minutes.

5. The preparation method according to claim 1, characterized in that: The step of using a rough rolling mill to perform rough rolling on the continuous casting billet to obtain a strip billet comprises: controlling the starting rolling temperature of the rough rolling to be 1160-1180° C., the final rolling temperature of the rough rolling to be 1090-1120° C., and using a rough rolling mill to perform rough rolling on the continuous casting billet to obtain a strip billet; The thickness of the strip obtained by rough rolling is 28-40 mm, and the number of rough rolling passes is 7.

6. The preparation method according to claim 1, characterized in that: The method of using a finishing mill to finish-roll the strip to obtain a hot-rolled steel strip comprises: controlling the start rolling temperature of the finishing rolling to be 1060-1110° C., the final rolling temperature of the finishing rolling to be 880-920° C., and using a finishing mill to finish-roll the strip to obtain a hot-rolled steel strip; Among them, the thickness of the hot-rolled steel strip obtained by finish rolling is 1.5-4.0 mm. The finish rolling adopts a 7-stand finishing rolling unit, and the rolling temperature of each stand is: 1028-1068°C for the first stand, 999-1039°C for the second stand, 977-1015°C for the third stand, 951-991°C for the fourth stand, 935-973°C for the fifth stand, 916-958°C for the sixth stand, and 892-942°C for the seventh stand.

7. The preparation method according to claim 1, characterized in that: The cooling treatment of the hot-rolled steel strip and coiling the cooled hot-rolled steel strip into a steel coil specifically comprises: The hot-rolled steel strip transported on the laminar cooling roller is cooled, wherein the cooling method of the hot-rolled steel strip on the laminar cooling roller is rear-stage sparse cooling, and the upper and lower header cooling water flow ratio during the cooling process is 4:6; and the coiling temperature is controlled to be 500-540°C, and the cooled hot-rolled steel strip is coiled into a steel coil by a coiler.

8. A steel coil for photovoltaic support, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 7.

9. The steel coil according to claim 8, characterized in that: The microstructure of the steel coil is ferrite and bainite, wherein the proportion of ferrite is 66-76% and the proportion of bainite is 24-34%.

10. The steel coil according to claim 9, characterized in that: The steel coil has a yield strength of ≥420MPa, a tensile strength of ≥550MPa, an elongation after fracture of ≥28%, and passes a 180°d=0 cold bending test; After the steel coil is periodically immersed in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate of the steel coil is ≤28% relative to that of Q355B ordinary steel.

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