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: 0.05 percent to 0.07 percent of C, 0.65 percent to 0.75 percent of Si, 0.61 percent to 0.70 percent of Mn, 0.066 percent to 0.075 percent of P, 0.0061 percent to 0.0070 percent of S, 0.13 percent to 0.18 percent of Cu, 2.5 percent to 2.7 percent of Cr, 0.036 percent to 0.045 percent of Ti, 0.21 percent to 0.24 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 brackets are important supporting structures of photovoltaic power stations. Their service environment is harsh, changeable and highly corrosive. Photovoltaic brackets need to withstand static loads, wind loads, snow loads and other external effects during their service.

[0003] At present, the raw materials used for photovoltaic brackets are mainly Q235 and Q355 hot-dip galvanized steel parts with yield strength levels of 235MPa and 355MPa respectively. They have low strength and cannot meet the requirements of lightweight and easy installation. They also require post-maintenance and have high cost of use over the entire life cycle. In addition, the hot-dip galvanizing process seriously pollutes the environment.

[0004] During the service life, a dense protective rust layer can be formed on the surface of weathering steel photovoltaic brackets, which can greatly improve its corrosion resistance. The rust layer can heal itself after damage, and no subsequent pickling, painting and maintenance are required. Therefore, the use of weathering steel to manufacture photovoltaic brackets has the advantages of energy saving and environmental protection. In order to adapt to the development trend of photovoltaic power stations, weathering steel for photovoltaic brackets should have the advantages of high strength, light weight, high corrosion resistance, long life, easy forming, easy welding, and low cost. Existing weathering steel products cannot fully meet these requirements.

[0005] So far, no reports have been found on low-alloy corrosion-resistant steel for photovoltaic brackets with good forming properties 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 good forming performance, good welding performance, high strength and excellent corrosion resistance.

[0007] According to one aspect of the present invention, there is provided a method for preparing a high-formability 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: 0.05%-0.07%, Si: 0.65%-0.75%, Mn: 0.61%-0.70%, P: 0.066%-0.075%, S: 0.0061%-0.0070%, Cu: 0.13%-0.18%, Cr: 2.5%-2.7%, Ti: 0.036%-0.045%, Alt: 0.21%-0.24%, and the rest are Fe and unavoidable impurities, and the continuous casting billet also needs to satisfy Mn / Si≥0.80.

[0015] Furthermore, the continuous casting billet obtained by pretreatment is specifically: obtaining the continuous casting billet through molten iron pretreatment desulfurization, top and bottom composite blowing converter smelting, LF and RH refining and slab continuous casting; the thickness of the continuous casting billet is 180-230mm.

[0016] 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;

[0017] The furnace discharge temperature of the continuous casting billet is 1200-1220° C., and the cumulative furnace residence time of the continuous casting billet is 180-210 minutes.

[0018] 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 1150-1170° C., the final rolling temperature of the rough rolling is controlled to be 1080-1110° C., and the continuous casting billet is rolled with a rough rolling mill to obtain a strip billet;

[0019] Among them, the thickness of the strip obtained by rough rolling is 28-40mm, the rough rolling is performed in 7 passes, and the reduction rate of each pass is: 15.3-16.2% for the first pass, 16.1-17.3% for the second pass, 17.0-20.0% for the third pass, 20.8-23.3% for the fourth pass, 21.6-25.9% for the fifth pass, 25.8-33.2% for the sixth pass, and 34.4-47.6% for the seventh pass.

[0020] 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 1020-1070° C., the final rolling temperature of the finishing rolling is controlled to be 870-910° C., and the finishing mill is used to finish-roll the strip to obtain a hot-rolled steel strip;

[0021] 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 reduction rate of each stand is: 44.1-56.6% for the first stand, 38.1-47.4% for the second stand, 31.8-37.8% for the third stand, 23.3-32.0% for the fourth stand, 20.1-27.6% for the fifth stand, 15.8-19.0% for the sixth stand, and 9.8-16.3% for the seventh stand.

[0022] Furthermore, the step of cooling the hot-rolled steel strip and coiling the cooled hot-rolled steel strip into a steel coil specifically comprises:

[0023] 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 cooling, and the upper and lower header cooling water flow ratio during the cooling process is 8:10; and the coiling temperature is controlled to be 580-620°C, and the cooled hot-rolled steel strip is coiled into a steel coil by a coiler.

[0024] The present invention also provides a high-formability steel coil for a photovoltaic bracket, which is prepared by any of the preparation methods described above.

[0025] Furthermore, the sum of the grades of various types of coarse and fine non-metallic inclusions in the steel coil is ≤ grade 2;

[0026] The steel coil has a yield strength of ≥460MPa, a tensile strength of ≥600MPa, an elongation after fracture of ≥23%, and is qualified in a 180°d=a cold bending test;

[0027] The steel coil was heated to an initial concentration of 0.01 mol / L NaHSO 3 After 72 hours of periodic immersion in the solution, the corrosion rate relative to Q355B ordinary steel is ≤28%;

[0028] When the straight seam electric welded steel pipe processed from the steel coil is completely flattened (completely in contact with the relative pipe wall), the parent material has no cracks.

[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, easy manufacturing, easy forming, easy welding, 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 the parent material after flattening is shown in a complete flattening (complete contact with the pipe wall) test of a straight seam electric welded steel pipe sample obtained by using the steel coil according to an embodiment of the present invention. 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: 0.05%-0.07%, Si: 0.65%-0.75%, Mn: 0.61%-0.70%, P: 0.066%-0.075%, S: 0.0061%-0.0070%, Cu: 0.13%-0.18%, Cr: 2.5%-2.7%, Ti: 0.036%-0.045%, Alt: 0.21%-0.24%, and the rest are Fe and unavoidable impurities.

[0045] The tensile strength of the steel coil prepared by the preparation method of the embodiment of the present invention is above 600 MPa and has high formability.

[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 an effective and economical way to improve the strength of steel is to increase the C content. However, as the C content increases, the plasticity, impact toughness, welding performance, forming performance, and corrosion resistance of the steel will decrease. In order to make the tensile strength of the steel strip of the embodiment of the present invention reach more than 600MPa and have high forming performance, and comprehensively consider the 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 0.05%-0.07%.

[0048] Si is not a precious alloying 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 the toughness of the material 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 600MPa, and comprehensively consider the processing performance, welding performance and corrosion resistance, while taking into account the economy, the embodiment of the present invention controls the Si content in the range of 0.65%-0.75%.

[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 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 600MPa, and comprehensively consider the processing performance and welding performance, while taking into account the economy, the embodiment of the present invention controls the Mn content in the range of 0.61%-0.70%.

[0050] It has been found in practice that the solid solution strengthening effect of P in steel is second only to C, which 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.3 P 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 formability of steel. In order to make the tensile strength of the steel strip of the embodiment of the present invention reach more than 600MPa, and comprehensively consider the processing performance, welding performance and corrosion resistance, while taking into account the economy, the embodiment of the present invention controls the P content in the range of 0.066%-0.075%.

[0051] It has been found in practice that a higher S content can cause "hot brittleness" defects in steel during hot working. 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, so the S content should be reduced as much as possible. However, if the S content is controlled too low, it will increase manufacturing costs and reduce production efficiency. Taking into account the uniformity of mechanical properties, processing properties and corrosion resistance of the high-formed 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 within the range of 0.0061%-0.0070%.

[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 at an anodic level. It is also enriched in the rust layer, changing the structure of the rust layer and preventing Cl- from invading the matrix, which can effectively improve the corrosion resistance of the steel. However, Cu has a low melting point (1083°C) and is prone to segregation at grain boundaries during the heating process of the continuous casting billet. Excessive Cu content can lead to network crack defects during hot rolling. Cu is also a relatively precious alloying element, and excessive Cu content can lead to increased product costs. Taking into account the hot working performance, surface quality and corrosion resistance of the high-formable steel strip in the embodiment of the present invention, while taking into account the economy, the Cu content in the embodiment of the present invention is controlled within 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 cost of the alloy. In order to make the tensile strength of the steel strip of the embodiment of the present invention reach more than 600MPa, 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 2.5%-2.7%.

[0054] It has been found in practice that 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 steel. 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 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, too high a Ti content will increase the difficulty of photovoltaic bracket processing and reduce processing efficiency. Taking into account the strength, welding performance, processing performance and use performance of the high-forming steel strip in the embodiment of the present invention, the embodiment of the present invention controls the Ti content in the range of 0.036%-0.045%.

[0055] It has been found in practice that in the marine atmosphere, Al and Si have a synergistic effect, making the generated rust layer have a strong barrier effect against corrosive media and moisture. The fine AlN formed by Al and N can inhibit the growth of austenite grains during the heating process of continuous casting billets, has the effect of refining grains, and can improve the strength, toughness and welding performance of steel. However, too high Al content will lead to the formation of more Al 2 O 3 Inclusions, on the one hand, reduce the purity of steel and the impact performance, corrosion resistance and surface quality of the steel strip, and on the other hand, are very easy to block the nozzle during continuous casting, increase the difficulty of production, reduce production efficiency, and increase the alloy cost and manufacturing cost. Taking into account the strength, welding performance, processing performance, corrosion resistance and surface quality of the high-formable steel strip of 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 Alt content in the range of 0.21%-0.24%.

[0056] The continuous casting in step S001 also needs to satisfy Mn / Si≥0.80.

[0057] It has been found in practice that if Mn / Si is less than 0.80, the oxygen content in the weld is high and the weld metallographic structure is abnormal, which significantly reduces the low-temperature impact toughness and sometimes cracks of different lengths can be observed. Considering the welding performance of the high-forming steel strip in the embodiment of the present invention, the embodiment of the present invention controls Mn / Si≥0.80.

[0058] The selection of the above-mentioned C, Si, Mn, P, S, Cu, Cr, Ti and 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-formability low-alloy corrosion-resistant steel for photovoltaic brackets has high purity, high strength and excellent cold processing performance.

[0059] The selection of the above-mentioned Si, P, S, Cu, Cr, and Alt element contents has a synergistic effect. By controlling the content of each element within the above-mentioned range, a dense inner rust layer can be formed on the surface of the steel matrix, so that the high-formability low-alloy corrosion-resistant steel for photovoltaic brackets has high corrosion resistance and meets the service requirements of photovoltaic brackets. There is no need for subsequent pickling, painting and maintenance, which is energy-saving and environmentally friendly.

[0060] The above-mentioned C, Mn, S, Cu, Alt element contents and the selection of Mn / Si have a synergistic effect. By controlling the content of each element and Mn / Si within the above-mentioned range, defects such as hot-rolled network cracks can be avoided, so that the high-formability low-alloy corrosion-resistant steel for photovoltaic brackets has excellent hot processing properties, high surface quality and excellent welding properties, which can meet the stringent processing and service requirements of photovoltaic brackets.

[0061] The content of all the above elements and the selection of Mn / Si have a synergistic effect. By controlling the content of all the elements and Mn / Si within the above range, the high-formability low-alloy corrosion-resistant steel for photovoltaic brackets has low processing difficulty, high production efficiency, low manufacturing cost and short delivery cycle.

[0062] 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 and RH refining and slab continuous casting; the thickness of the continuous casting billet is 180-230mm.

[0063] 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.

[0064] 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;

[0065] The furnace discharge temperature of the continuous casting billet is 1200-1220°C, and the cumulative furnace residence time of the continuous casting billet is 180-210 minutes.

[0066] It has been found in practice that if the furnace temperature of the continuous casting billet is lower than 1200°C, the austenite grains can be refined, but the thermoplasticity of the continuous casting billet is poor, the deformation resistance is high, and the thermal deformation is difficult, which will lead to a low subsequent rolling mill operating rate; if the furnace temperature of the continuous casting billet is higher than 1220°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 temperature of the continuous casting billet to be 1200-1220°C. If the cumulative furnace 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 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 cumulative furnace time of the continuous casting billet to be 180-210 minutes.

[0067] Among them, step S003 uses a rough rolling mill to perform rough rolling on the continuous casting billet to obtain a strip billet. Specifically, the starting rolling temperature of the rough rolling is controlled to be 1150-1170°C, the final rolling temperature of the rough rolling is controlled to be 1080-1110°C, and the continuous casting billet is rolled by the rough rolling mill to obtain a strip billet.

[0068] It has been found in practice that multiple recrystallizations through rough rolling can effectively refine austenite grains and obtain 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 1150-1170°C, and the rough rolling final rolling temperature to 1080-1110°C.

[0069] Among them, the thickness of the strip obtained by rough rolling is 28-40mm, the rough rolling is 7 passes, and the reduction rate of each pass is: 15.3-16.2% for the first pass, 16.1-17.3% for the second pass, 17.0-20.0% for the third pass, 20.8-23.3% for the fourth pass, 21.6-25.9% for the fifth pass, 25.8-33.2% for the sixth pass, and 34.4-47.6% for the seventh pass, as shown in Table 1 for details.

[0070] Table 1 Rough rolling process (reduction rate of each pass) of a steel coil for photovoltaic support

[0071] Rolling pass Pass 1 Pass 2 Pass 3 Pass 4 Pass 5 Pass 6 Pass 7 Pass reduction rate (%) 15.3-16.2 16.1-17.3 17.0-20.0 20.8-23.3 21.6-25.9 25.8-33.2 34.4-47.6

[0072] It has been found in practice that if the strip is too thick and the pass reduction rate of rough rolling is too small, partial recrystallization is likely to occur, causing mixed crystal phenomenon, which has an adverse effect on the uniformity of the mechanical properties of the finished steel strip, and at the same time 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 and the pass reduction rate of rough rolling is too large, it is not conducive to improving the strip shape quality, and will increase the rolling load and rolling energy consumption of the rough rolling mill, which is not conducive to the smooth rolling. At the same time, it is impossible to ensure the finishing rolling start temperature required for rolling the 1.5-4.0mm thin finished steel strip of the present invention, and it may even increase the rolling load and rolling energy consumption of the finishing mill. Taking the above effects into consideration, the embodiment of the present invention controls the strip thickness to be 28-40mm. According to the mechanical performance parameters of the rough rolling mill, the continuous casting billet and the strip thickness, it can be calculated that the reasonable rolling pass of the rough rolling mill is 7 passes, and the rough rolling pass reduction rate of the embodiment of the present invention is controlled within the range of Table 1.

[0073] 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 1020-1070°C, the final rolling temperature of the finishing rolling is controlled to be 870-910°C, and the finishing mill is used to finish rolling the strip to obtain a hot-rolled steel strip.

[0074] 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 1020-1070°C in the embodiment of the present invention.

[0075] 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 870-910℃.

[0076] 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, and the reduction rate of each stand is: the first stand (F1) 44.1-56.6%, the second stand (F2) 38.1-47.4%, the third stand (F3) 31.8-37.8%, the fourth stand (F4) 23.3-32.0%, the fifth stand (F5) 20.1-27.6%, the sixth stand (F6) 15.8-19.0%, and the seventh stand (F7) 9.8-16.3%, see Table 2.

[0077] Table 2 Finishing process of steel coil for photovoltaic support (reduction rate of each rack)

[0078] Rack number F1 F2 F3 F4 F5 F6 F7 Pass reduction rate (%) 44.1-56.6 38.1-47.4 31.8-37.8 23.3-32.0 20.1-27.6 15.8-19.0 9.8-16.3

[0079] 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.

[0080] It has been found in practice that if the reduction rate of each stand of the finishing mill is lower than the lower limit specified in Table 2, uneven grains will occur and plasticity will be reduced. If the reduction rate is higher than the upper limit specified in Table 2, the deformation resistance and load of each stand of the finishing mill will increase, leading to equipment hazards. Taking the above factors into consideration, the reduction rate of each stand of the finishing mill is determined as shown in Table 2.

[0081] 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 cooling, and the upper and lower manifold cooling water flow ratio during the cooling process is 8:10; and the coiling temperature is controlled to be 580-620°C, and the cooled hot-rolled steel strip is coiled into a steel coil by a coiler.

[0082] It has been found in practice that compared with other cooling methods, the rear 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, plasticity and cold forming properties of the finished steel strip well matched.

[0083] In addition, the use of the back-end 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 in the embodiment of the present invention is back-end cooling.

[0084] It has been found in practice that if the cooling water flow ratio of the upper and lower headers is higher or lower than 8:10, 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 cooling water flow ratio of the upper and lower headers in the embodiment of the present invention is controlled to be 8:10.

[0085] 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 580-620℃.

[0086] 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.

[0087] Embodiment 1-embodiment 3:

[0088] The preparation methods of Examples 1 to 3 of the present invention include the following steps:

[0089] First, a continuous casting billet is obtained by pre-treatment of molten iron for desulfurization, top and bottom composite blowing in converter, LF and RH refining, and slab continuous casting. The chemical compositions of the continuous casting billets obtained in Examples 1 to 3 are shown in Table 3.

[0090] Table 3 Chemical composition (mass percentage) of the continuous casting slabs of Examples 1 to 3 of the present invention

[0091] C Si Mn P S Cr Cu Ti Alt Mn / Si (ratio) Example 1 0.062 0.72 0.69 0.071 0.0066 2.62 0.16 0.044 0.23 0.95 Example 2 0.066 0.66 0.68 0.067 0.0063 2.58 0.15 0.042 0.22 1.03 Example 3 0.055 0.69 0.63 0.073 0.0068 2.67 0.17 0.037 0.21 0.91

[0092] 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 4-Table 5, and the properties of the obtained steel coil are shown in Table 6.

[0093] Table 4 Heating and rough rolling process parameters of Examples 1 to 3 of the present invention

[0094]

[0095] Table 5 Finishing rolling, cooling and coiling process parameters of Examples 1 to 3 of the present invention

[0096]

[0097]

[0098] Table 6 Performance of steel coils obtained from Examples 1 to 3 of the present invention

[0099]

[0100] It can be seen from Table 3 to Table 6 that the chemical composition, heating, rough rolling, finishing rolling, cooling and other process parameters of the steel coils prepared in Examples 1-3 of the present invention and general weathering steel are significantly different, and the microstructure and various properties are also significantly different. A high-formability low-alloy corrosion-resistant steel for photovoltaic brackets in an 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, easy manufacturing, easy forming, easy welding, low cost, high efficiency, free painting, maintenance-free, energy saving, and environmental protection.

[0101] 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, and Alt, and controls Mn / Si, continuous casting billet discharge temperature, furnace residence time, rough rolling start and final rolling temperature, rolling pass, strip billet thickness, pass reduction rate, finishing rolling start and final rolling temperature, rolling pass, finished product thickness, reduction rate of each stand, cooling method, upper and lower header cooling water flow ratio and coiling temperature, so that the sum of the grades of various coarse and fine non-metallic inclusions in the obtained finished steel is ≤2 levels; and the yield strength of the obtained steel coil is ≥460MPa, the tensile strength is ≥600MPa, the elongation after fracture is ≥23%, the 180°d=a cold bending test is qualified, and the initial concentration of NaHSO is 0.01mol / L 3 After 72 hours of periodic immersion in the solution, the corrosion rate is ≤28% relative to Q355B ordinary steel. Figure 2 As shown, when the straight seam electric welded steel pipe sample processed by the steel coil according to the embodiment of the present invention is completely flattened (completely in contact with the relative pipe wall), there is no crack in the base material.

[0102] The steel coil prepared by the preparation method of the embodiment of the present invention has low content of harmful and impurity elements and pure steel. It has high strength and can reduce weight by 22% by replacing Q235B galvanized sheet, with a significant lightweight effect. It has strong corrosion resistance and can meet the service requirements of photovoltaic brackets. 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., and has a low Mn content, so the alloy cost is low. No need for post-pickling, painting and maintenance, energy saving, environmental protection, short delivery cycle and low use cost.

[0103] 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, easy manufacturing, easy forming, easy welding, low cost, high efficiency, painting-free, maintenance-free, energy-saving, and environmental protection.

[0104] 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.

[0105] Among them, the sum of the grades of various coarse and fine non-metallic inclusions in the steel coil is ≤ Grade 2.

[0106] The yield strength of the steel coil is ≥460MPa, the tensile strength is ≥600MPa, the elongation after fracture is ≥23%, and the 180°d=a cold bending test is qualified.

[0107] The steel coil was exposed to an initial concentration of 0.01 mol / L NaHSO 3 After 72 hours of periodic immersion in the solution, the corrosion rate relative to Q355B ordinary steel is ≤28%;

[0108] When the straight seam electric welded steel pipe specimen processed from the steel coil is completely flattened, there is no crack in the base material.

[0109] 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: 0.05%-0.07%, Si: 0.65%-0.75%, Mn: 0.61%-0.70%, P: 0.066%-0.075%, S: 0.0061%-0.0070%, Cu: 0.13%-0.18%, Cr: 2.5%-2.7%, Ti: 0.036%-0.045%, Alt: 0.21%-0.24%, and the rest are Fe and unavoidable impurities, and the continuous casting billet also needs to satisfy Mn / Si≥0.

80.

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

3. 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 1200-1220° C., and the cumulative furnace residence time of the continuous casting billet is 180-210 minutes.

4. The preparation method according to claim 1, characterized in that: The method of using a rough rolling mill to rough-roll the continuous casting billet to obtain a strip billet specifically comprises controlling the starting rolling temperature of the rough rolling to be 1150-1170° C., the final rolling temperature of the rough rolling to be 1080-1110° C., and using a rough rolling mill to roll the continuous casting billet to obtain a strip billet.

5. The preparation method according to claim 4, characterized in that: The thickness of the strip obtained by rough rolling is 28-40mm, and the rough rolling is performed in 7 passes. The reduction rate of each pass is: 15.3-16.2% for the first pass, 16.1-17.3% for the second pass, 17.0-20.0% for the third pass, 20.8-23.3% for the fourth pass, 21.6-25.9% for the fifth pass, 25.8-33.2% for the sixth pass, and 34.4-47.6% for the seventh pass.

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 specifically comprises controlling the start rolling temperature of the finishing rolling to be 1020-1070°C, the final rolling temperature of the finishing rolling to be 870-910°C, and using a finishing mill to finish-roll the strip to obtain a hot-rolled steel strip.

7. The preparation method according to claim 6, characterized in that: 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 reduction rate of each stand is: 44.1-56.6% for the first stand, 38.1-47.4% for the second stand, 31.8-37.8% for the third stand, 23.3-32.0% for the fourth stand, 20.1-27.6% for the fifth stand, 15.8-19.0% for the sixth stand, and 9.8-16.3% for the seventh stand.

8. 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 cooling, and the cooling water flow ratio of the upper and lower headers is 8:10; and the coiling temperature is controlled to be 580-620°C, and the cooled hot-rolled steel strip is coiled into a steel coil by a coiler.

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

10. The steel coil according to claim 9, characterized in that: The sum of the grades of various coarse and fine non-metallic inclusions in the steel coil is ≤ Grade 2; The steel coil has a yield strength of ≥460MPa, a tensile strength of ≥600MPa, an elongation after fracture of ≥23%, and is qualified in a 180°d=a 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 relative to Q355B ordinary steel is ≤28%; When the straight seam electric welded steel pipe processed from the steel coil is completely flattened (completely in contact with the relative pipe wall), the parent material has no cracks.

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