Steel coil for photovoltaic support and method for manufacturing thereof

Abstract

The application relates to a steel coil for a photovoltaic support and a preparation method thereof, and the preparation method comprises the following steps: obtaining a continuous casting blank; rolling the continuous casting blank to obtain a hot-rolled steel strip; and coiling the steel strip into a steel coil; according to mass percentage, the continuous casting blank comprises the following components: C: 0.02%-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 is Fe and inevitable impurities. The steel coil prepared by the application can better meet the new requirements of the development of the photovoltaic support.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hot-rolled steel strip manufacturing, and particularly relates to a steel coil for photovoltaic support and a preparation method thereof. BACKGROUND

[0002] Photovoltaic power generation has the characteristics of no noise, no pollution, simple maintenance, etc., and is a green and environmentally friendly industry with broad development space and application prospect.

[0003] The photovoltaic support is an important supporting and protective structure of the photovoltaic power generation device. In order to prevent the photovoltaic support from corroding, Q235 and Q355 material coils are currently mostly used for galvanizing, but the production of hot-dipped galvanized products will pollute the environment.

[0004] Weathering steel is an ideal product for manufacturing photovoltaic supports. In order to improve the strength and corrosion resistance, a high content of valuable alloying elements such as V, Nb, Ni, Cu, etc. is generally added in the production of weathering steel for photovoltaic supports in China at present, which increases the production cost, and the plasticity is insufficient, which cannot meet the harsh processing requirements of photovoltaic supports. It is of great significance to develop weathering steel for photovoltaic supports with high strength, high corrosion resistance, high plasticity and low cost.

[0005] At present, there is no related report on low-alloy corrosion-resistant steel for photovoltaic supports with high plasticity and its manufacturing method. SUMMARY

[0006] In order to solve all or part of the above problems, the present application aims to provide a steel coil for photovoltaic support and a preparation method thereof. The hot-rolled steel coil produced by the preparation method of the present application has small difficulty; the obtained steel coil has high plasticity, high strength, good forming and welding performance, and excellent corrosion resistance.

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

[0008] obtaining a continuous casting billet by pretreatment;

[0009] heating and heat preserving the continuous casting billet;

[0010] coarsely rolling the continuous casting billet by a coarse rolling mill to obtain a strip billet;

[0011] finely rolling the strip billet by a fine rolling mill 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 in terms of 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%, Al: 0.23%-0.27%, Alt: 0.25%-0.28%, and the balance of Fe and inevitable impurities.

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

[0016] Further, the continuous casting billet is obtained by molten iron pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining and slab continuous casting.

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

[0018] The continuous casting billet has a tapping temperature of 1210-1230℃, and a cumulative furnace residence time of 180-210 minutes.

[0019] Further, the rough rolling of the continuous casting billet by the rough rolling mill to obtain a strip billet comprises: controlling the rough rolling start temperature to be 1160-1180℃, and the rough rolling finish temperature to be 1090-1120℃, and rolling the continuous casting billet by the rough rolling mill to obtain a strip billet.

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

[0021] Further, the finish rolling of the strip billet by the finish rolling mill to obtain a hot-rolled steel strip comprises: controlling the finish rolling start temperature to be 1060-1110℃, and the finish rolling finish temperature to be 880-920℃, and finish rolling the strip billet by the finish rolling mill to obtain a hot-rolled steel strip.

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

[0023] Further, the hot-rolled steel strip is cooled and coiled into a steel coil, and the cooling process is specifically as follows:

[0024] The hot-rolled steel strip is cooled on the laminar cooling roller, wherein the cooling mode of the hot-rolled steel strip on the laminar cooling roller is sparse cooling in the later stage, the cooling water flow ratio of the upper and lower headers is 4:6, and the coiling temperature is controlled at 500-540 DEG C.

[0025] The application further provides a steel coil for a photovoltaic support, which is prepared by the preparation method.

[0026] Further, the microstructure of the steel coil is ferrite and bainite, wherein the proportion of the ferrite is 66-76%, and the proportion of the bainite is 24-34%.

[0027] The yield strength of the steel coil is greater than or equal to 420 MPa, the tensile strength is greater than or equal to 550 MPa, the elongation after fracture is greater than or equal to 28%, and the 180° d=0 cold bending test is qualified.

[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 is less than or equal to 28% relative to that of Q355B ordinary steel.

[0029] According to the above technical solution, the steel coil for a photovoltaic support and the preparation method thereof have the following beneficial effects.

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

[0031] The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate the principles of the application and, together with the description, serve to explain the application.

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0033] Figure 1 The flow chart of the preparation method of the embodiments of the application;

[0034] Figure 2 The schematic diagram of the sample of the steel coil prepared by the embodiments of the application after the cold bending test. DETAILED DESCRIPTION

[0035] For the purpose of fully understanding the object, features and effects of the present application, the present application will be described in detail by the following specific embodiments. The process method of the present application adopts the conventional method or device in the art except the following content. The following terms have the meanings commonly understood by the skilled in the art unless otherwise specified.

[0036] When a numerical range is disclosed herein, the range is to be construed as continuous, and includes the minimum and maximum values of the range, as well as every value between the minimum and maximum values. Further, when the range is for integers, 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 are to be understood as including any and all sub-ranges subsumed therein.

[0037] A method for preparing a steel coil for a photovoltaic support according to an embodiment of the present application, as shown in FIG. 1, comprises the following steps: Figure 1

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

[0039] Step S002: heating and holding treatment on the continuous casting billet;

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

[0041] Step S004: finish rolling of the strip billet by a finish rolling mill to obtain a hot-rolled steel strip; and

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

[0043] In step S001, the continuous casting billet comprises 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 is Fe and inevitable impurities.

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

[0046] Wherein the reasons for the restriction of each chemical element in the embodiments of the present application are as follows:

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

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

[0049] It is found in practice that Mn can form a substitutional solid solution in steel, and play a solid solution strengthening role, so as to linearly increase the yield strength and tensile strength. Mn is an austenite forming element, and has the effect of stabilizing austenite, which can reduce the austenite transformation temperature (Ar3), increase the ferrite nucleation rate, and reduce the grain growth rate, i.e. has the effect of refining the grains. However, the increase of the content of Mn can increase the C equivalent (Ceq) of the steel, which is not conducive to the welding performance. In order to make the tensile strength of the steel strip in the embodiments of the present application reach more than 550 MPa, and comprehensively consider the plasticity, processing performance and welding performance, while taking into account the economy, the content of Mn in the embodiments of the present application is controlled in the range of 0.71%-0.80%.

[0050] It is found in practice that the solid solution strengthening effect of P in steel is only second to C, which can effectively improve the atmospheric corrosion resistance of the steel. Among the alloying elements for improving the corrosion resistance, P is the element with the highest cost performance. However, P is easy to form and precipitate Fe3P in steel, which increases the brittleness of the steel, and is not conducive to improving the welding performance of the steel. The diffusion speed of P in γ iron and α iron is small, and P is easy to form segregation, which has an adverse effect on the forming performance of the steel. In order to make the tensile strength of the steel strip in the embodiments of the present application reach more than 550 MPa, and comprehensively consider the plasticity, processing performance, welding performance and corrosion resistance, while taking into account the economy, the content of P in the embodiments of the present application is controlled in the range of 0.076%-0.085%.

[0051] It is found in practice that higher S content can cause the steel to produce "hot brittleness" defects, and adding Mn to the steel to form MnS plastic inclusions can reduce the harmful effects of S. However, the MnS extending along the rolling direction during rolling is easy to form banded structure in the steel strip, which can reduce the transverse impact toughness and forming performance of the steel strip, and also cause the anisotropy of mechanical properties. S is harmful to the corrosion resistance of the steel, and the sulfide 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 be increased and the production efficiency will be reduced. Considering the uniformity of mechanical properties, processing performance and corrosion resistance of the high plasticity steel strip of the embodiment, and also taking into account the economy and production efficiency, the S content of the embodiment is controlled in the range of 0.0071%-0.0080%.

[0052] It is found in practice that Cu forms precipitates on the surface of the steel, and as a cathode causes the surface of the steel to be anodically passivated, and is enriched in the rust layer to change the structure of the rust layer, prevent Cl - from invading the matrix, so Cu is an effective element for improving the corrosion resistance of the steel. However, the melting point of Cu is relatively low (1083℃), and it is easy to segregate at the grain boundary during the heating of the continuous casting billet, and too high Cu content can cause the formation of network cracks during hot rolling. Cu is also a relatively valuable alloying element, and too high Cu content can cause the product cost to increase. Considering the hot working performance, surface quality and corrosion resistance of the high plasticity steel strip of the embodiment, and also taking into account the economy, the Cu content of the embodiment is controlled in the range of 0.13%-0.18%.

[0053] It is found in practice that Cr has a solid solution strengthening effect, can improve the hardenability and strength of the steel, can form a dense and uniform rust layer containing fine α-FeOOH on the surface of the matrix, accelerate the development of the electrochemical corrosion product to the thermodynamic stable state, block the further penetration of the corrosion medium to the matrix, and reduce the corrosion rate of the steel. However, when the Cr content is too high, carbides will be precipitated at the grain boundaries, which will reduce the plasticity and toughness of the steel, and also make the forming performance and welding performance worse, and increase the alloy cost. In order to make the tensile strength of the steel strip of the embodiment reach 550MPa or more, and considering the corrosion resistance, plasticity and toughness, processing performance and welding performance, and also taking into account the economy, the Cr content of the embodiment is controlled in the range of 2.2%-2.4%.

[0054] It is found in practice that TiN formed by Ti and N can inhibit austenite grain growth during continuous casting billet heating, which is beneficial to improve the strength and toughness of the steel and the welding performance. Ti and C form nanoscale TiC precipitates during hot rolling, which has the effects of fine-grain strengthening and precipitation strengthening, and can improve the strength and toughness of the steel. If the Ti content is high, on the one hand, coarse TiN precipitates are easy to form, which become stress concentration points and micro-crack sources, reducing the forming and fatigue performance of the photovoltaic support, on the other hand, the recovery rate of Ti is unstable, and the mechanical properties fluctuate greatly, so the high Ti content will increase the processing difficulty of the photovoltaic support and reduce the processing efficiency. Considering the strength and toughness, welding performance, processing performance and use performance of the high plasticity steel strip of the embodiment, the Ti content is controlled in the range of 0.046%-0.055% in the embodiment.

[0055] It is found in practice that fine AlN formed by Al and N can inhibit austenite grain growth during continuous casting billet heating, which has the effect of refining grains, and can improve the strength and toughness of the steel and the welding performance. In the marine atmospheric environment, Al and Si have a synergistic effect, so that the generated rust layer has a strong barrier effect on corrosion medium and moisture. However, too high Al content will lead to the formation of more Al2O3 inclusions, which on the one hand reduces the purity of the steel and the impact performance, corrosion resistance and surface quality of the steel strip, on the other hand, it is very easy to block the water gap during continuous casting, which increases the production difficulty, reduces the production efficiency, and increases the alloy cost and manufacturing cost. Considering the strength and toughness, welding performance, processing performance, impact performance, corrosion resistance and surface quality of the high plasticity steel strip of the embodiment, and taking into account the production difficulty, production efficiency and economy, the AlS content is controlled in the range of 0.23%-0.27% and the Alt content is controlled in the range of 0.25%-0.28% in the embodiment.

[0056] In step S001, the continuous casting billet also needs to satisfy Als / Alt≥0.95. It is found in practice that the higher the Als / Alt ratio, the more significant the beneficial effects of Al on refining grains and improving the strength and toughness of the steel, so Als / Alt should be as high as possible. According to experience, Als / Alt≥0.95 is controlled in the embodiment.

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

[0058] The selection of the Si, P, S, Cu, Cr, Als and Alt element contents has a synergistic effect, by controlling the element contents in the above ranges, a dense inner rust layer can be formed on the surface of the steel matrix, the high plasticity low alloy corrosion-resistant steel for photovoltaic support has high corrosion resistance, can meet the processing and service requirements of the photovoltaic support, and does not need post-acid pickling, coating and maintenance, has the advantages of energy saving and environmental protection.

[0059] The selection of the C, Mn, S, Cu, Als and Alt has a synergistic effect, by controlling the element contents in the above ranges, defects such as hot-rolled network cracks can be avoided, the high plasticity low alloy corrosion-resistant steel for photovoltaic support has excellent hot working performance and high surface quality, and can meet the harsh processing and service requirements of the photovoltaic support.

[0060] The selection of all the element contents and Als / Alt has a synergistic effect, by controlling all the element contents and Als / Alt in the above ranges, the high plasticity low alloy corrosion-resistant steel for photovoltaic support has small processing difficulty, high production efficiency, low manufacturing cost and short delivery cycle.

[0061] In the step S001, the continuous casting billet is obtained by molten iron pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining and slab continuous casting.

[0062] It is found in practice that, under the premise that the width and length of the continuous casting billet are determined, the thicker the continuous casting billet is, the higher the yield and the material yield are, but the larger the rolling mill load is, and the greater the fluctuations of the finish rolling temperature, microstructure and mechanical properties of the finished steel strip in the length direction are, and the thickness of the continuous casting billet is also limited by the maximum steel coil outer diameter allowed by the coiler. Considering the above influences comprehensively, the thickness of the continuous casting billet is controlled to be 180-230mm in the embodiment of the application.

[0063] In the step S002, the heating and heat preservation treatment of the continuous casting billet further includes: loading the continuous casting billet into a walking beam furnace; and heating and heat preserving the continuous casting billet in the walking beam furnace.

[0064] In the step S002, the heating and heat preservation treatment of the continuous casting billet further includes: loading the continuous casting billet into a walking beam furnace; and heating and heat preserving the continuous casting billet in the walking beam furnace.

[0065] It is found through practice that if the continuous casting billet has an out-of-furnace temperature lower than 1210 DEG C, the austenite grains can be refined, but the continuous casting billet has poor hot plasticity, high deformation resistance and difficult hot deformation, thus leading to low subsequent rolling mill operation rate; if the continuous casting billet has an out-of-furnace temperature higher than 1230 DEG C, the hot plasticity of the continuous casting billet is improved, the deformation resistance is reduced, the hot deformation is easy, and the corresponding subsequent rolling mill operation rate is improved, but the austenite grains are prone to coarsening. In consideration of the above influences, the out-of-furnace temperature of the continuous casting billet is controlled to be 1210-1230 DEG C in the embodiment of the application. If the cumulative residence time of the continuous casting billet is shorter than 180 minutes, the structure is not easy to be homogenized, the rolling energy consumption is high, and equipment accidents are prone to occur; if the cumulative residence time of the continuous casting billet is longer than 210 minutes, oxidation and decarburization are prone to occur, the corresponding energy consumption is increased, and the rolling mill operation rate and production efficiency are reduced. In consideration of the above influences, the out-of-furnace temperature of the continuous casting billet is controlled to be 1210-1230 DEG C, and the cumulative residence time is controlled to be 180-210 minutes in the embodiment of the application.

[0066] In step S003, the continuous casting billet is coarsely rolled by a coarse rolling mill to obtain a strip billet, specifically: the coarsely rolling starting temperature is controlled to be 1160-1180 DEG C, the coarsely rolling final temperature is controlled to be 1090-1120 DEG C, and the continuous casting billet is rolled by the coarse rolling mill to obtain the strip billet.

[0067] It is found through practice that the main metallurgical purpose of coarse rolling is to destroy the as-cast structure of the continuous casting billet, effectively refine the austenite grains through multiple recrystallizations, and obtain the austenite structure with uniform and small grains. If the coarsely rolling starting temperature is too high, the austenite grains are not uniform, leading to differences in the strip billet structure and affecting the uniformity of the mechanical properties of the finished product. If the coarsely rolling starting temperature is too low, the strip billet shape control is difficult, the rolling mill load and rolling energy consumption are increased, and the rolling is not easy to proceed. In consideration of the above influences, the coarsely rolling starting temperature is controlled to be 1160-1180 DEG C, and the coarsely rolling final temperature is controlled to be 1090-1120 DEG C in the embodiment of the application.

[0068] In the embodiment of the application, the thickness of the strip billet obtained through coarse rolling is 28-40 mm, and the rolling pass of coarse rolling is 7 passes.

[0069] It is found through practice that if the strip blank is too thick, the cumulative reduction rate and pass reduction rate of rough rolling will be reduced, partial recrystallization is prone to occur, mixed crystal phenomenon is caused, and the uniformity of the mechanical properties of the finished steel strip is adversely affected; meanwhile, the rolling load and rolling energy consumption of the finishing rolling mill train are increased, and the stability of the finishing rolling is affected. If the strip blank is too thin, the strip blank flatness quality is not improved, the rolling load and rolling energy consumption of the rough rolling mill are increased, the smooth rolling is not conducive, and the finishing rolling open rolling temperature required for rolling the 1.5-4.0 mm thin specification finished steel strip cannot be ensured, and the rolling load and rolling energy consumption of the finishing rolling mill train are even likely to be increased. Considering the above factors comprehensively, the thickness of the strip blank is controlled to be 28-40 mm in the embodiment of the present application. According to the force and energy parameters of the rough rolling mill, the continuous casting blank and the thickness of the strip blank, the reasonable rolling pass of the rough rolling mill can be calculated to be 7 passes.

[0070] In the step S004, the strip blank is finished rolling by the finishing rolling mill train to obtain the hot-rolled steel strip, specifically: the open rolling temperature of the finishing rolling is controlled to be 1060-1110℃, the finish rolling temperature is 880-920℃, and the strip blank is finished rolling by the finishing rolling mill train to obtain the hot-rolled steel strip.

[0071] It is found through practice that if the open rolling temperature of the finishing rolling is too high, the first rack (F1) and the second rack (F2) are prone to partial recrystallization, leading to mixed crystal problem and abnormal fluctuation of the microstructure and mechanical properties of the finished steel strip; if the open rolling temperature of the finishing rolling is too low, the desired finish rolling temperature cannot be ensured. Considering the above factors comprehensively, the open rolling temperature of the finishing rolling is controlled to be 1060-1110℃ in the embodiment of the present application.

[0072] It is found through practice that if the finish rolling temperature of the finishing rolling is too high, the microstructure of the finished steel strip will be coarsened, and the strength and toughness will be reduced; if the finish rolling temperature of the finishing rolling is too low, the strength of the finished steel strip will be increased, the plasticity will be reduced, the strength and plasticity matching will be unreasonable, the rolling stability of the finishing rolling mill train will be reduced, the thickness precision, width precision and cross-sectional shape of the steel strip will be difficult to control, and the steel strip will be seriously rolled and damaged. Considering the above factors comprehensively, the finish rolling temperature of the finishing rolling is controlled to be 880-920℃ in the embodiment of the present application.

[0073] In the step S004, the strip blank is finished rolling by the finishing rolling mill train to obtain the hot-rolled steel strip, specifically: the open rolling temperature of the finishing rolling is controlled to be 1060-1110℃, the finish rolling temperature is 880-920℃, and the strip blank is finished rolling by the finishing rolling mill train to obtain the hot-rolled steel strip.

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

[0075] Rack No. F1 F2 F3 F4 F5 F6 F7 Finish rolling temperature (°C) 1028-1068 999-1039 977-1015 951-991 935-973 916-958 892-942

[0076] Wherein, the finishing rolling adopts 7-stand finishing rolling mill set depending on actual equipment configuration, and the finished steel strip thickness is 1.5-4.0mm which is selected by the user.

[0077] It is found through practice that if the finishing rolling temperature is too high, the front stand is prone to partial recrystallization, resulting in mixed crystal problem, finished steel strip organization difference, and abnormal fluctuation of mechanical properties; if the finishing rolling temperature is too low, the strength and plasticity of the finished steel strip are not reasonably matched, and the rolling stability of the finishing rolling mill set is reduced, resulting in difficulty in controlling the thickness precision, width precision and cross section shape of the steel strip, and even the steel strip is rolled off and the equipment is damaged. Considering the above factors, the finishing rolling temperature of the embodiment of the present application is controlled in the range of Table 1.

[0078] Wherein, the step S005 cools the hot-rolled steel strip and winds the cooled hot-rolled steel strip into a steel coil, specifically: cooling the hot-rolled steel strip conveyed on the laminar cooling roller way, wherein the cooling mode of the hot-rolled steel strip on the laminar cooling roller way is sparse cooling in the rear section, the cooling water flow rate ratio of the upper header tank to the lower header tank is 4:6 during the cooling process; and controlling the winding temperature to be 500-540℃, and winding the cooled hot-rolled steel strip into a steel coil by using a winding machine.

[0079] It is found through practice that compared with other cooling modes, the sparse cooling mode in the rear section is beneficial to the analysis of ferrite, the ferrite grain size is uniform, the carbon content in the ferrite grain can be reduced, and the movable dislocation density can be increased, so that the strength, toughness, plasticity and cold forming performance of the finished steel strip are well matched.

[0080] In addition, the sparse cooling mode in the rear section can make the 1.5-4.0mm thin specification finished steel strip of the embodiment of the present application run smoothly on the laminar cooling roller way, and be successfully wound, avoiding rolling accidents such as steel stacking during winding. Considering the above factors, the cooling mode of the hot-rolled steel strip on the laminar cooling roller way in the embodiment of the present application is sparse cooling in the rear section.

[0081] It is found through practice that if the cooling water flow rate ratio of the upper header tank to the lower header tank is higher or lower than 4:6, a large difference will be generated in the cooling rate of the upper and lower surfaces of the steel strip, resulting in fluctuation of the organization and mechanical properties, and increasing the difficulty of shape control. Considering the above factors, the cooling water flow rate ratio of the upper header tank to the lower header tank in the embodiment of the present application is controlled to be 4:6.

[0082] It is found through practice that, by reasonably controlling the coiling temperature, the γ→α phase transition temperature can be appropriately reduced, the α phase nucleation rate is increased, and the ferrite grains are refined. Meanwhile, the proportion of bainite in the structure is appropriately increased, the bainite grain size is smaller than that of the ferrite, is about 1 μm, and has a higher dislocation density, so that the comprehensive mechanical properties of the steel strip can be improved. In addition, reasonably controlling the coiling temperature is also a necessary measure to reduce the plate shape and coiling shape control difficulty. Considering the above factors, the coiling temperature in the embodiments of the present application is controlled to be 500-540 ℃.

[0083] The present application is further illustrated by the following examples, but the present application is not limited to the examples. The experimental methods in the following examples are carried out according to the conventional methods and conditions.

[0084] Examples 1-3:

[0085] The preparation method of the embodiments 1-3 of the present application comprises the following steps:

[0086] Firstly, the continuous casting billets are obtained by hot metal pretreatment desulphurization, top and bottom combined blowing converter smelting, LF refining and slab continuous casting. The chemical compositions of the continuous casting billets obtained in the embodiments 1-3 are shown in Table 2.

[0087] Table 2 Chemical compositions of the continuous casting billets of the embodiments 1-3 of the present application (mass percent)

[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 hot-rolled steel strips are obtained by heating, rough rolling, finishing rolling and cooling of the continuous casting billets, and the hot-rolled steel coils are obtained by coiling. The process parameters of each process are shown in Tables 3-4, and the properties of the obtained steel coils are shown in Table 5.

[0090] Table 3 Process parameters of heating and rough rolling of the embodiments 1-3 of the present application

[0091]

[0092] Table 4 Process parameters of finishing rolling, cooling and coiling of the embodiments 1-3 of the present application

[0093]

[0094] Table 5 Properties of the steel coils obtained in the embodiments 1-3 of the present application

[0095]

[0096] As can be seen from Tables 2-5, the chemical composition, heating, rough rolling, finish rolling, cooling and other process parameters of the inventive examples 1-3 and the general weathering steel are significantly different, and the microstructure and various properties are also significantly different. The steel coil prepared by the inventive examples can better meet the new requirements of high strength, lightweight, high corrosion resistance, long service life, high plasticity, easy manufacturing, low cost, high efficiency, coating-free, maintenance-free, energy saving, environmental protection and other photovoltaic support development.

[0097] The preparation method of the inventive example optimizes the content of elements such as C, Si, Mn, P, S, Cu, Cr, Ti, Als, Alt, and controls Als / Alt, continuous casting billet discharge temperature, residence time, rough rolling and finish rolling temperature, rolling pass, strip thickness, finish rolling and finish rolling temperature, rolling pass, finished product thickness, rolling temperature, cooling method, upper and lower header cooling water flow ratio, and coiling temperature, so that the microstructure of the obtained finished steel material is composed of 66-76% ferrite and 24-34% bainite; and the obtained steel coil has a yield strength of ≥420 MPa, a tensile strength of ≥550 MPa, and an elongation after fracture of ≥28%; as shown in the figure, the steel coil sample of the inventive example passes 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 is ≤28% relative to the corrosion rate of Q355B ordinary steel. Figure 2

[0098] The steel coil prepared by the preparation method of the inventive example has low harmful and impurity element content, pure steel quality, high strength, can reduce weight by 20% instead of Q235B galvanized sheet, and has significant lightweight effect. The steel coil has strong corrosion resistance and can meet the coating-free service requirements of photovoltaic supports. The steel coil has excellent forming performance and can meet the harsh processing requirements of photovoltaic supports. The P and Al contents are moderate, and the Cu and Ti contents are low, which avoids the adverse effects of the elements on plasticity, weldability, surface quality and other properties, and the mechanical properties are stable, the manufacturing difficulty is small, and the production efficiency is high. The steel coil does not contain valuable alloy elements such as Ni, Nb, V and Mo, has low Mn content, and has low alloy cost. The steel coil does not need post-acid pickling, coating and maintenance, is energy-saving and environmentally friendly, has a short delivery cycle, and has low use cost.

[0099] The steel coil prepared by the preparation method of the inventive example can better meet the new requirements of high strength, lightweight, high corrosion resistance, long service life, high plasticity, easy manufacturing, low cost, high efficiency, coating-free, maintenance-free, energy saving, environmental protection and other photovoltaic support development.

[0100] The inventive example also provides a steel coil for photovoltaic supports, which is prepared by the preparation method of any one of the above examples.

[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 greater than or equal to 420 MPa, the tensile strength is greater than or equal to 550 MPa, the elongation after fracture is greater than or equal to 28%, and the 180° d=0 cold bending test is qualified.

[0103] The corrosion rate of the steel coil after periodic immersion in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours is less than or equal to 28% relative to that of Q355B ordinary steel.

[0104] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; 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 application. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for manufacturing a steel coil for a photovoltaic support, characterized in that, include: Continuous casting billets are obtained through pretreatment; The continuously cast billet is heated and held at a constant temperature. The continuously cast billet is rough-rolled using a roughing mill to obtain a strip billet; The strip billet is finished by a finishing mill to obtain hot-rolled steel strip; as well as The hot-rolled steel strip is cooled and then coiled into a steel coil. The continuously cast billet, by mass percentage, consists of the following components: C: 0.02%-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%, with the remainder being Fe and unavoidable impurities; The process of cooling the hot-rolled steel strip and then coiling it into a steel coil involves: cooling the hot-rolled steel strip transported on a laminar flow cooling roller conveyor, wherein the cooling method on the laminar flow cooling roller conveyor is sparse cooling in the latter part, and the flow rate ratio of the cooling water in the upper and lower manifolds is 4:6 during the cooling process; and controlling the coiling temperature at 500-540℃, and using a coiler to coil the cooled hot-rolled steel strip into a steel coil. The microstructure of the steel coil consists of ferrite and bainite, with ferrite accounting for 66-76% and bainite accounting for 24-34%.

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

95.

3. The preparation method according to claim 1, characterized in that, The process of obtaining a continuously cast billet through pretreatment specifically involves: desulfurization of molten iron through pretreatment, smelting in a top-and-bottom combined blowing converter, refining in an LF refining process, and continuous casting of slabs to obtain a continuously cast billet; the thickness of the continuously cast billet is 180-230mm.

4. The preparation method according to claim 1, characterized in that, The heating and heat preservation treatment of the continuous casting billet further includes: loading the continuous casting billet into a walking beam furnace; and heating and heat preservation treatment of the continuous casting billet in the walking beam furnace; The furnace exit temperature of the continuously cast billet is 1210-1230℃, and the cumulative furnace dwell time of the continuously cast billet is 180-210 minutes.

5. The preparation method according to claim 1, characterized in that, The process of using a roughing mill to rough-roll the continuously cast billet to obtain a strip billet specifically involves: controlling the initial rolling temperature of the roughing mill to be 1160-1180℃ and the final rolling temperature of the roughing mill to be 1090-1120℃, and using a roughing mill to roll the continuously cast billet to obtain a strip billet. The thickness of the strip obtained by rough rolling is 28-40 mm, and the rough rolling process consists of 7 passes.

6. The preparation method according to claim 1, characterized in that, The process of using a finishing mill to finish rolling the strip billet to obtain hot-rolled steel strip specifically involves: controlling the initial rolling temperature of the finishing mill to be 1060-1110℃ and the final rolling temperature of the finishing mill to be 880-920℃, and using a finishing mill to finish rolling the strip billet to obtain hot-rolled steel strip. The thickness of the hot-rolled steel strip obtained by finishing rolling is 1.5-4.0 mm. The finishing rolling adopts a 7-stand finishing mill. The rolling temperature of each stand is as follows: 1st stand 1028-1068℃, 2nd stand 999-1039℃, 3rd stand 977-1015℃, 4th stand 951-991℃, 5th stand 935-973℃, 6th stand 916-958℃, and 7th stand 892-942℃.

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

8. The steel coil according to claim 7, characterized in that, The steel coil has a yield strength ≥420MPa, tensile strength ≥550MPa, elongation after fracture ≥28%, and passes the 180°d=0 cold bending test. After the steel coil was periodically immersed in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate relative to Q355B ordinary steel was ≤28%.

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