High-toughness low-alloy corrosion-resistant steel for photovoltaic support and manufacturing method thereof

Abstract

The application discloses a kind of high tough low alloy corrosion-resistant steel for photovoltaic support and manufacturing method thereof, solve the technical problems such as high manufacturing cost, poor comprehensive performance, low production efficiency.The composition of the high tough low alloy corrosion-resistant steel includes: C: 0.17%-0.20%, Si: 0.80%-0.95%, Mn: 0.10%-0.19%, P: 0.031%-0.039%, S: 0.0020%-0.0030%, Cu: 0.13%-0.18%, Cr: 3.1%-3.3%, Ti: 0.010%-0.025%, Alt: 0.02%-0.06%, T[O]: 0.0010%-0.0020%, N: 0.0030%-0.0055%, B: 0.0021%-0.0031%, the rest is Fe and inevitable impurities, high tough low alloy corrosion-resistant steel meets Ti / N≥3.4.The manufacturing method of high tough low alloy corrosion-resistant steel includes smelting, continuous casting, continuous casting blank red sending hot charging, heating, heat preservation, rough rolling, finish rolling, cooling and coiling.The application can reduce manufacturing cost, improve steel performance and improve production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of hot-rolled steel strip manufacturing technology, specifically relating to a high-strength, high-toughness, low-alloy corrosion-resistant steel for photovoltaic brackets and its manufacturing method. Background Technology

[0002] Currently, driven by dual-carbon and energy transition goals, countries worldwide are placing great emphasis on the development of renewable energy. Solar energy is the most abundant renewable energy source and is also currently the safest and cleanest energy source. Solar photovoltaic power generation is a major highlight in the new energy field. Since 2006, the global installed capacity of solar photovoltaic power has been on the rise, demonstrating strong development momentum.

[0003] Photovoltaic (PV) mounting systems are specialized structural components designed for placing, installing, and securing solar cell modules within a photovoltaic (PV) power generation system. Due to the scarcity of land resources, deserts, Gobi, wastelands, tidal flats, nearshore areas, coal and oil mining subsidence areas, and saline-alkali lands are becoming the primary sites for PV power generation systems. In these open, harsh outdoor environments, PV mounting systems are constantly subjected to wind, rain, snow, strong sunlight, and extreme temperatures, as well as bearing their own weight, wind loads, snow loads, and seismic loads. To ensure the long-term stable and reliable operation of PV mounting systems in such harsh environments, the steel used in these systems must possess excellent corrosion resistance and high strength and toughness, meeting requirements for corrosion resistance, tensile strength, compressive strength, earthquake resistance, and sand erosion resistance.

[0004] Currently, photovoltaic (PV) mounting systems primarily use ordinary Q235B or Q355B hot-dip galvanized steel sheets, which have low strength, are structurally heavy, and have poor low-temperature impact toughness, making them prone to brittle fracture in cold service environments. Furthermore, hot-dip galvanizing severely pollutes the environment. During high-temperature galvanizing, the NH4Cl in the flux readily volatilizes and decomposes upon heating, generating large amounts of dense NH4Cl fumes and irritating gases such as NH3 and HCl, polluting the environment. It also produces zinc dust and zinc vapor, posing a health hazard to operators. In addition, hot-dip galvanized sheets are easily damaged by collisions and scratches during transportation and construction, leading to galvanized layer peeling off and high subsequent maintenance costs.

[0005] Weathering steel is becoming an ideal material for manufacturing photovoltaic brackets due to its unique corrosion resistance, high cost performance, and advantages such as environmental protection and energy saving. However, the existing weathering steel's corrosion resistance, strength, toughness, hardness, and cost cannot yet meet the service and economic requirements of photovoltaic brackets.

[0006] Chinese patent CN202211337425.2 discloses a high-strength, low-cost weathering steel for photovoltaic brackets, its preparation method, and its application. Its chemical composition includes: C: ≤0.10%, Si: 0.02~0.50%, Mn: 0.80~2.00%, P≤0.030%, S≤0.005%, Cr: 0.20~0.80%, Cu: 0.20~0.60%, W: 0.05~0.50%, and Als: 0.010~0.050%. The preparation method employs the TMCP process, where the steel plate is rapidly cooled to 100~300℃; tempering temperature is 150~400℃, and holding time is 20~40 min. Compared to ordinary Q345B steel, it exhibits a corrosion rate ≤45%, yield strength ≥690MPa, tensile strength 820~920MPa, elongation ≥18%, and low-temperature impact energy ≥200J.

[0007] However, the steel used in photovoltaic brackets has a high content of the precious alloying element Cu, which easily leads to network crack defects during hot rolling and increases costs. It also contains the expensive rare and strategic metal W, further increasing alloy costs. The steel plate has a low final cooling temperature, making it difficult to control plate and coil shape. Tempering heat treatment is required to reduce residual stress in the steel plate, increasing manufacturing costs and extending the production cycle. Compared to ordinary carbon steel Q345B, its corrosion rate is 33-45%, indicating lower corrosion resistance. The applicable temperature range for low-temperature impact resistance is not clearly defined, making material selection difficult for users.

[0008] Chinese patent CN202410138488 discloses a weathering hot-rolled steel strip and its production method. The weathering steel strip has the following chemical composition: C: 0.03-0.09%, Si: 0.05-0.30%, Mn: 0.4-1.8%, P: 0.04-0.07%, S: ≤0.0050%, Cr: 1.0-4.0%, Cu: 0.20-0.50%, Al: 0.01-0.05%, Ti: 0.09-0.15%, N: ≤0.0060%, yield strength ≥690MPa, tensile strength ≥800MPa, elongation ≥14%, low-temperature impact energy at -40℃ ≥60J, weathering resistance index I ≥8.0, and corrosion rate ≤35% relative to Q355B ordinary low alloy structural steel.

[0009] However, the aforementioned photovoltaic bracket steel has a high phosphorus (P) content, resulting in severe segregation in the cast billet. This leads to poor plasticity and low-temperature toughness, making it prone to various cracks and exacerbating intergranular corrosion. Simultaneously, the high content of the precious alloying element Cu increases product cost and easily generates network crack defects during hot rolling. The high Ti content easily forms coarse TiN precipitates, which become stress concentration points and microcrack initiations, reducing the formability and fatigue performance of the photovoltaic bracket. Furthermore, the unstable Ti recovery rate leads to large fluctuations in mechanical properties, increasing the processing difficulty and reducing processing efficiency of the photovoltaic bracket.

[0010] Chinese patent CN202210677545.0 discloses a high-strength, high-formability, ultra-resistant atmospheric corrosion steel and its manufacturing method. Its chemical composition includes: C: 0.04–0.10%, Si ≤ 0.50%, Mn: 0.20–1.80%, P ≤ 0.03%, S ≤ 0.01%, Al ≤ 0.30%, Cu: 0.10–0.60%, Cr: 1.5–4.5%, Ti: 0.04–0.18%, N ≤ 0.008%, Ni: 0–0.26%, Nb: 0–0.048%, V: 0–0.12%, Mg: 0–0.003%, and Si+2Ni ≥ 0.10%. The yield strength is ≥ 700 MPa, tensile strength is ≥ 800 MPa, yield-to-tensile ratio is ≤ 0.90, elongation is ≥ 18%, cold bending performance meets the requirement of 180°D = 1t bending, and low-temperature impact toughness is above 60 J at -20℃.

[0011] However, excessively high Mn content in the aforementioned photovoltaic support steel reduces its plasticity and cold forming properties. High Al content makes the nozzle prone to clogging during continuous casting. High Cu content easily forms copper brittle cracks and peeling defects on the strip surface, deteriorating surface quality; Cu is also a valuable element, increasing alloy costs. High Ti content weakens its precipitation strengthening effect and significantly affects the steel's low-temperature toughness. Ni is an important strategic material and expensive; adding Ni significantly increases alloy costs. Excessively high Nb content causes surface cracks and corner cracks in the continuously cast billet; excessively high V content reduces the steel's weld toughness; Nb and V are valuable elements, significantly increasing alloy costs. Mg has a boiling point of 1107℃; when Mg alloys are added to molten steel, Mg rapidly vaporizes in large quantities, resulting in extremely low yield and poor economic efficiency. Low-temperature impact toughness only meets the requirements for use at -20℃, making it difficult to meet the service requirements of photovoltaic supports in extremely cold regions.

[0012] In summary, the steel used in existing photovoltaic (PV) mounting systems contains a significant amount of precious metals, increasing production costs, and the steel also exhibits poor corrosion resistance and toughness. Furthermore, existing PV mounting systems are difficult to manufacture, have high production costs, and low production efficiency, requiring further improvement. Summary of the Invention

[0013] In order to solve all or part of the above problems, the purpose of this invention is to provide a high-strength, high-toughness, low-alloy corrosion-resistant steel for photovoltaic brackets and its manufacturing method, which can reduce manufacturing costs, achieve lightweighting, and improve the corrosion resistance and toughness of steel, while also reducing the production difficulty of photovoltaic brackets and improving production efficiency.

[0014] In a first aspect, the present invention provides a high-strength, high-toughness, low-alloy corrosion-resistant steel for photovoltaic brackets. The composition of the high-strength, high-toughness, low-alloy corrosion-resistant steel by mass percentage includes: C: 0.17%-0.20%, Si: 0.80%-0.95%, Mn: 0.10%-0.19%, P: 0.031%-0.039%, S: 0.0020%-0.0030%, Cu: 0.13%-0.18%, Cr: 3.1%-3.3%, Ti: 0.010%-0.025%, Alt: 0.02%-0.06%, T[O]: 0.0010%-0.0020%, N: 0.0030%-0.0055%, B: 0.0021%-0.0031%, with the remainder being Fe and unavoidable impurities.

[0015] The high-strength, high-toughness, low-alloy corrosion-resistant steel meets the requirement of Ti / N ≥ 3.4.

[0016] Optionally, the high-strength, high-toughness, low-alloy corrosion-resistant steel has the following properties:

[0017] Grain size ≥ 11;

[0018] Yield strength ≥750MPa, tensile strength ≥850MPa, elongation after fracture ≥18%, strength-ductility product ≥15.3 (GPa·%), qualified for 180°d=a cold bending test, impact absorption energy at -40℃ ≥120J, Brinell hardness ≥245.

[0019] After 72 hours of cyclic immersion in a NaHSO3 solution with an initial concentration of 0.01 mol / L, the corrosion rate relative to Q355B ordinary steel is ≤28%.

[0020] Secondly, the present invention provides a method for manufacturing high-strength, high-toughness, low-alloy corrosion-resistant steel for photovoltaic brackets, comprising the following steps:

[0021] S1, through hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining, RH refining and slab continuous casting, to obtain a continuously cast billet with a thickness of 180-230mm;

[0022] S2, the continuously cast billet is heated and loaded into a walking beam furnace for heating and heat preservation;

[0023] S3 uses a roughing mill to roll the continuously cast billet to obtain a strip billet;

[0024] S4 uses a finishing mill to roll the strip billet to obtain hot-rolled steel strip;

[0025] S5, hot-rolled steel strip is cooled during transport on a laminar flow cooling roller conveyor;

[0026] S6, hot-rolled steel strip is wound into hot-rolled steel coils by a coiler.

[0027] Optionally, in S2, the continuous casting billet charging temperature is controlled to be ≥550℃, and the time from billet discharge to loading into the walking beam furnace is controlled to be ≤8 hours.

[0028] Optionally, in S2, the heating time of the continuously cast billet in the temperature range of 550℃-700℃ is controlled to be 60-67.5 minutes, the heating time in the temperature range of 700℃-1170±10℃ is controlled to be 75-90 minutes, and the holding time in the temperature range of 1160℃-1180℃ is controlled to be 45-52.5 minutes, and the furnace exit temperature of the continuously cast billet is controlled to be 1160℃-1180℃, and the cumulative furnace dwell time is controlled to be 180-210 minutes.

[0029] Optionally, in S3, the continuously cast billet is rough rolled in 7 passes, and the rough rolling start temperature is controlled at 1110℃-1130℃ and the rough rolling finish temperature is controlled at 1040℃-1080℃.

[0030] Optionally, in S4, the strip is finished rolled by a 7-stand finishing mill, and the finishing rolling start temperature is controlled at 980℃-1030℃, the finishing rolling finish temperature is controlled at 830℃-870℃, and the hot-rolled steel strip thickness is controlled at 4.0-6.0mm.

[0031] Optionally, in S5, the cooling method of the hot-rolled steel strip on the laminar flow cooling roller table is front-end densified laminar flow cooling, and the flow ratio of the cooling water in the upper and lower manifolds is controlled to be 10:12.

[0032] Optionally, in S6, the hot-rolled steel strip winding temperature is controlled at 550℃-590℃ during the hot-rolled steel strip winding process.

[0033] As can be seen from the above technical solution, the high-strength, high-toughness, low-alloy corrosion-resistant steel for photovoltaic brackets and its manufacturing method provided by the present invention have the following advantages:

[0034] This low-alloy corrosion-resistant steel has low levels of harmful and impurity elements, resulting in pure steel, fine grains, and high strength and toughness. Replacing Q235B galvanized steel can reduce weight by 36%, demonstrating significant lightweighting effects. The high hardness of this low-alloy corrosion-resistant steel also provides strong resistance to wind and sand erosion in photovoltaic supports used in the Gobi Desert. Furthermore, this low-alloy corrosion-resistant steel exhibits high corrosion resistance, with a corrosion rate ≤28% compared to ordinary Q355B steel.

[0035] Meanwhile, the low-alloy corrosion-resistant steel has moderate P and Al content, low Cu and Ti content, and no Mg element with a low boiling point, which avoids its adverse effects on plasticity, toughness, weldability, hot-rolled surface quality, etc., making the mechanical properties of the low-alloy corrosion-resistant steel more stable, and making smelting and continuous casting easier, with less difficulty in controlling plate and coil shape, making the steel and photovoltaic brackets easier to manufacture, and increasing production efficiency.

[0036] Furthermore, this low-alloy corrosion-resistant steel does not contain expensive rare and strategic metals such as wrought iron (W), nor does it contain precious alloying elements such as nickel (Ni), nitrogen (Nb), v (V), and molybdenum (Mo). Its low manganese (Mn) content effectively reduces alloy costs. Simultaneously, photovoltaic brackets made from this low-alloy corrosion-resistant steel require no subsequent acid pickling, painting, or maintenance, offering advantages such as energy saving, environmental friendliness, short delivery cycles, and low operating costs.

[0037] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0038] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the technical solutions of the present invention, and do not constitute a limitation on the technical solutions of the present invention.

[0039] Figure 1 This is a flowchart illustrating the manufacturing method of high-strength, high-toughness, low-alloy corrosion-resistant steel in an embodiment of the present invention.

[0040] Figure 2 This is a typical microstructure of high-strength, high-toughness, low-alloy corrosion-resistant steel under a scanning electron microscope, as shown in the embodiments of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be arbitrarily combined with each other.

[0042] like Figure 1 , Figure 2 The illustration shows an embodiment of the present invention, which discloses a high-strength, high-toughness, low-alloy corrosion-resistant steel for photovoltaic brackets. The composition of this high-strength, high-toughness, low-alloy corrosion-resistant steel, by mass percentage, includes: C: 0.17%-0.20%, Si: 0.80%-0.95%, Mn: 0.10%-0.19%, P: 0.031%-0.039%, S: 0.0020%-0.0030%, Cu: 0.13%-0.18%, Cr: 3.1%-3.3%, Ti: 0.010%-0.025%, Alt: 0.02%-0.06%, T[O]: 0.0010%-0.0020%, N: 0.0030%-0.0055%, B: 0.0021%-0.0031%, with the remainder being Fe and unavoidable impurities. Simultaneously, the low-alloy corrosion-resistant steel satisfies a Ti / N ratio ≥ 3.4.

[0043] The reasons for the restrictions on each chemical element in this embodiment are as follows:

[0044] Practice has shown that increasing the carbon (C) content is an effective and economical way to improve the strength of steel. However, as the C content increases, the steel's plasticity, impact toughness, weldability, formability, and corrosion resistance decrease. To achieve a tensile strength of over 850 MPa for the steel strip in this embodiment, and considering processing performance, weldability, and corrosion resistance while also maintaining economic efficiency, this invention controls the C content within the range of 0.17%-0.20%.

[0045] Practice has shown that Si is not a precious alloying element. Its solid solution strengthening coefficient in ferrite is higher than that of Mn. Si is very effective in improving strength and corrosion resistance. However, excessively high Si content reduces the toughness of the material and is not conducive to improving weldability. To achieve a tensile strength of over 850 MPa for the steel strip of this invention, and considering processing performance, weldability, and corrosion resistance, while also taking into account economic efficiency, the Si content of this invention is controlled within the range of 0.80%-0.95%.

[0046] Practice has shown that manganese (Mn) can form a substitutional solid solution in steel, resulting in solid solution strengthening and a linear increase in yield strength and tensile strength. Mn is an austenite-forming element, stabilizing austenite, lowering the austenite transformation temperature, increasing the ferrite nucleation rate, and reducing grain growth rate—in other words, refining the grain size. However, increasing the Mn content increases the carbon equivalent in the steel, which is detrimental to weldability. To achieve a tensile strength of over 850 MPa in the steel strip of this invention, while comprehensively considering processing performance, weldability, and economic efficiency, the Mn content is controlled within the range of 0.10%-0.19%.

[0047] Practice has shown that phosphorus (P) has the second-highest solid solution strengthening effect in steel after carbon (C), effectively improving its resistance to atmospheric corrosion. Among many alloying elements that improve corrosion resistance, P offers the best cost-effectiveness. However, P easily forms and precipitates Fe3P in steel, increasing its brittleness and hindering its weldability. P diffuses slowly in γ-ferric and α-ferric iron, easily forming segregation, which negatively impacts the steel's formability. To achieve a tensile strength of over 850 MPa in the steel strip of this invention, and considering processing performance, weldability, and corrosion resistance while also maintaining economic efficiency, the P content is controlled within the range of 0.031%-0.039%.

[0048] Practice has shown that high sulfur (S) content can lead to "hot brittleness" defects in steel. Adding manganese (Mn) to the steel to form MnS plastic inclusions can mitigate the harmful effects of S. However, during rolling, MnS extending along the rolling direction easily causes the steel strip to form a banded structure, reducing the transverse impact toughness and formability of the steel strip, while also leading to anisotropy in mechanical properties. S is detrimental to the corrosion resistance of steel, and sulfides in steel can become sources of rust. Therefore, 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. Considering the uniformity of mechanical properties, processing performance, and corrosion resistance of the high-strength and high-toughness steel strip of this invention, while also taking into account economy and production efficiency, this invention controls the S content in the range of 0.0020%-0.0030%.

[0049] Practical experience has shown that Cu forms precipitates on the surface of steel, acting as a cathode to cause anodic passivation of the steel surface, and accumulates in the rust layer, altering the rust layer structure and inhibiting Cl... - Cu penetrates the matrix, making it an effective element for improving the corrosion resistance of steel. However, Cu has a low melting point (1083℃) and tends to segregate at grain boundaries during the heating process of continuously cast billets. Excessive Cu content can lead to network crack defects during hot rolling. Cu is also a relatively expensive alloying element, and excessive Cu content increases product costs. Considering the hot working performance, surface quality, and corrosion resistance of the high-strength and tough steel strip of this invention, while also taking into account economic efficiency, this invention controls the Cu content within the range of 0.13%-0.18%.

[0050] Practice has shown that Cr has a solid solution strengthening effect, which can improve the hardenability and strength of steel. It can form a dense and uniform rust layer containing fine α-FeOOH on the matrix surface, accelerate the development of electrochemical corrosion products to a thermodynamically stable state, prevent the further penetration of corrosive media into the matrix, and reduce the corrosion rate of steel. However, when the Cr content is too high, carbides will precipitate at the grain boundaries, reducing the ductility and toughness of the steel, worsening its formability and weldability, and increasing the cost of the alloy. In order to achieve a tensile strength of over 850 MPa for the steel strip of this invention, and considering corrosion resistance, ductility and toughness, processing performance, weldability, and economic efficiency, the Cr content of this invention is controlled within the range of 3.1%-3.3%.

[0051] Practice has shown that TiN, formed by Ti and N, can inhibit austenite grain growth during the heating process of continuously cast billets, which is beneficial to improving the strength, toughness, and weldability of steel. Ti preferentially combines with N to form TiN, avoiding the formation of harmful BN, allowing B to fully exert its beneficial effects. If the Ti content is high, on the one hand, it is easy to form coarse TiN precipitates, which become stress concentration points and microcrack sources, reducing the forming and fatigue performance of photovoltaic brackets. On the other hand, the recovery rate of Ti is unstable, resulting in large fluctuations in mechanical properties, increasing the processing difficulty of photovoltaic brackets and reducing processing efficiency. Taking into account the strength, toughness, weldability, processing performance, and service performance of the high-strength and high-toughness steel strip of this invention, the Ti content is controlled in the range of 0.010%-0.025%.

[0052] Practice has shown that the fine AlN formed by Al and N can inhibit austenite grain growth during the heating process of continuously cast billets, thus refining the grains and improving the strength, toughness, and weldability of steel. Al preferentially combines with O to form Al2O3, preventing B from being oxidized and allowing B to fully exert its beneficial effects. However, excessively high Al content leads to the formation of more Al2O3 inclusions, which on the one hand reduces the purity of the steel and the impact resistance, corrosion resistance, and surface quality of the steel strip; on the other hand, it easily clogs the nozzle during continuous casting, increasing production difficulty, reducing production efficiency, and increasing alloy and manufacturing costs. Considering the strength, toughness, weldability, machinability, impact resistance, corrosion resistance, and surface quality of the high-strength and high-toughness steel strip of this invention, and taking into account production difficulty, efficiency, and economy, this invention controls the Alt content in the range of 0.02%-0.06%.

[0053] Practice has shown that oxygen is the heat source for converter steelmaking, oxidizing and removing impurities from molten steel. However, deoxidation is necessary in the later stages of steelmaking; otherwise, high oxygen levels will prevent continuous casting of the molten steel and will form a large number of oxidized inclusions, reducing the purity and deteriorating the steel's properties. Therefore, the oxygen content in the steel should be minimized. However, excessively low oxygen content will increase production difficulty, reduce production efficiency, and increase manufacturing costs. Considering the purity and overall performance of the high-tensile strength and toughness steel strip of this invention, and taking into account production difficulty, efficiency, and economy, this invention controls the T[O] content within the range of 0.0010%-0.0020%.

[0054] Practice has shown that nitrogen (N) is a harmful element in steel; excessively high N content reduces the purity of the steel and deteriorates its properties. Therefore, the N content in steel should be minimized. However, excessively low N content increases the difficulty of refining, reduces production efficiency, and increases manufacturing costs. Taking into account the purity and overall performance of the high-strength and high-toughness steel strip of this invention, while also considering production difficulty, efficiency, and economy, this invention controls the N content within the range of 0.0030%-0.0055%.

[0055] Practice has shown that trace amounts of boron (B) can improve the hardenability of steel, significantly increase its strength, and enhance its toughness. However, B is a segregating element, and when its content is high, it easily forms Fe3(B,C) and Fe... 23 The network precipitates composed of (B,C) are brittle and hard, weakening the bonds between the matrix components and negatively impacting the ductility and toughness of the steel. This effect is more pronounced when the number and size of the precipitates are large. Higher B content also increases manufacturing costs. Considering the strength, ductility, and toughness of the high-strength, high-toughness steel strip of this invention, while also taking economic factors into account, the B content is controlled within the range of 0.0021%-0.0031%.

[0056] Practical experience has shown that as the Ti / N ratio decreases, not all N in the steel can be fixed by Ti, and some N will combine with B to form harmful BN, thus failing to fully realize the beneficial effects of B in significantly improving the strength and toughness of the steel. Considering both the strength and toughness of the high-strength and high-toughness steel strip of this invention, the Ti / N ratio is controlled to be ≥3.4.

[0057] In this embodiment, the selection of C, Si, Mn, P, S, Cu, Cr, Ti, Alt, T[O], N, B, and Ti / N has a synergistic effect. By controlling the content of each element and Ti / N within the above range, the effects of solid solution strengthening, grain refinement strengthening, and phase transformation strengthening can be fully utilized, so that the high-strength and tough low-alloy corrosion-resistant steel for photovoltaic brackets has high purity, high strength and toughness, and excellent cold working performance.

[0058] Secondly, the selection of the contents of the above-mentioned elements Si, P, S, Cu, Cr, Alt, and T[O] has a synergistic effect. By controlling the contents of each element within the above range, a dense internal rust layer can be formed on the surface of the steel matrix, giving the high-strength and tough low-alloy corrosion-resistant steel high corrosion resistance. It does not require subsequent pickling, painting, and maintenance, and is energy-saving and environmentally friendly.

[0059] Meanwhile, the selection of C, Mn, S, Cu, Alt, and T[O] has a synergistic effect. By controlling the content of each element within the above range, defects such as hot-rolled network cracks can be avoided, and the high-strength, high-toughness, low-alloy corrosion-resistant steel for photovoltaic brackets has excellent hot working performance and high surface quality, which can meet the stringent processing and service requirements of photovoltaic brackets.

[0060] Moreover, the content of all the above elements and the selection of Ti / N have a synergistic effect. By controlling the content of all elements and Ti / N within the above range, the high-strength, high-toughness, low-alloy corrosion-resistant steel for photovoltaic brackets is easy to process, has high production efficiency, low manufacturing cost, and short delivery cycle.

[0061] The low-alloy corrosion-resistant steel in this embodiment has at least the following properties:

[0062] (1) The grain size of high-strength, high-toughness, low-alloy corrosion-resistant steel is ≥11 grade.

[0063] (2) The yield strength of high-strength and tough low-alloy corrosion-resistant steel is ≥750MPa, tensile strength is ≥850MPa, elongation after fracture is ≥18%, strength-ductility product is ≥15.3 (GPa·%), the cold bending test at 180°d=a is qualified, the impact absorption energy at -40℃ is ≥120J, and the Brinell hardness is ≥245.

[0064] (3) After being periodically immersed in a NaHSO3 solution with an initial concentration of 0.01 mol / L for 72 hours, the corrosion rate of high-strength and high-toughness low-alloy corrosion-resistant steel is ≤28% compared to ordinary Q355B steel.

[0065] like Figure 1 As shown, this embodiment also discloses a method for manufacturing high-strength, high-toughness, low-alloy corrosion-resistant steel for photovoltaic brackets, comprising the following steps:

[0066] S1 is obtained by hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining, RH refining and slab continuous casting.

[0067] S2, the continuously cast billet is heated and loaded into a walking beam furnace for heating and heat preservation;

[0068] S3 uses a roughing mill to roll the continuously cast billet to obtain a strip billet;

[0069] S4 uses a finishing mill to roll the strip billet to obtain hot-rolled steel strip;

[0070] S5, hot-rolled steel strip is cooled during transport on a laminar flow cooling roller conveyor;

[0071] S6, hot-rolled steel strip is wound into hot-rolled steel coils by a coiler.

[0072] In S1, the composition of the continuously cast billet by mass percentage is as follows: C: 0.17%-0.20%, Si: 0.80%-0.95%, Mn: 0.10%-0.19%, P: 0.031%-0.039%, S: 0.0020%-0.0030%, Cu: 0.13%-0.18%, Cr: 3.1%-3.3%, Ti: 0.010%-0.025%, Alt: 0.02%-0.06%, T[O]: 0.0010%-0.0020%, N: 0.0030%-0.0055%, B: 0.0021%-0.0031%, with the remainder being Fe and unavoidable impurities, and the Ti / N ratio in the continuously cast billet is ≥3.4.

[0073] In S1, the thickness of the continuously cast billet is 180-230mm. Practical experience has shown that, given a fixed width and length, a thicker billet results in higher output and yield, but also a greater mill load and greater fluctuations in the final rolling temperature, microstructure, and mechanical properties of the finished steel strip along its length. Furthermore, the billet thickness is limited by the maximum allowable outer diameter of the coiler. Therefore, considering all these factors, this embodiment controls the billet thickness to 180-230mm.

[0074] In S2, the charging temperature of the continuously cast billet is controlled to be ≥550℃, and the time from billet discharge to loading into the walking beam furnace is controlled to be ≤8 hours. Practice has shown that, under the premise of matching steelmaking and hot rolling capacity, planned timing, and stable production, a charging temperature of ≥550℃ for the hot-charged continuously cast billet significantly reduces energy consumption and oxidation loss, while also preventing cracking defects in the continuously cast billet.

[0075] If the charging temperature of the continuously cast billet is <550℃, energy consumption and oxidation loss will increase, and the tendency of the continuously cast billet to crack due to thermal stress and structural stress will be enhanced. Therefore, this invention controls the charging temperature of the continuously cast billet to ≥550℃.

[0076] If the time from billet tapping to furnace loading is ≤8 hours, the furnace loading temperature can be guaranteed to be ≥550℃, and the production efficiency is high. If the time from billet tapping to furnace loading is >8 hours, the furnace loading temperature cannot be guaranteed to be ≥550℃, and the production efficiency is low. Therefore, this invention controls the time from billet tapping to loading into the walking beam furnace to be ≤8 hours.

[0077] In S2, the heating time of the continuously cast billet is controlled to be 60-67.5 minutes in the temperature range of 550℃-700℃, 75-90 minutes in the temperature range of 700℃-1170±10℃, and 45-52.5 minutes in the temperature range of 1160℃-1180℃. The billet exit temperature is controlled to be 1160℃-1180℃, and the cumulative furnace dwell time is 180-210 minutes.

[0078] Practical experience has shown that the low-alloy corrosion-resistant steel in this invention has a unique chemical composition. Within the temperature range of 550℃-700℃, the continuously cast billet exhibits poor plasticity, and thermal stress exists on the surface and in the center due to the large temperature difference. If the heating time in this temperature range is less than 60 minutes, the risk of cracking due to thermal stress increases. If the heating time in this temperature range is longer than 67.5 minutes, oxidation loss, decarburization, energy consumption increase, and production decreases. Therefore, this invention controls the heating time of the continuously cast billet within the 550℃-700℃ temperature range to 60-67.5 minutes.

[0079] Practical experience has shown that the plasticity of continuously cast billets is improved within the temperature range of 700℃-1170±10℃, allowing for shorter heating times; however, thermal stress still exists. If the heating time within this temperature range is less than 75 minutes, the risk of cracking due to thermal stress increases. If the heating time exceeds 90 minutes, oxidation loss, decarburization, energy consumption, and production output increase. Therefore, this invention controls the heating time of continuously cast billets within the 700℃-1170±10℃ temperature range to 75-90 minutes.

[0080] Practice has shown that if the holding and tapping temperatures of the continuously cast billet are below 1160℃, the austenite grains can be refined, but the billet exhibits poor thermoplasticity, high deformation resistance, and difficulty in hot deformation, resulting in low mill operating rates. Conversely, if the holding and tapping temperatures are above 1180℃, the austenite grains tend to coarsen, but the billet's thermoplasticity increases, deformation resistance decreases, and it is prone to hot deformation, leading to high mill operating rates. Therefore, considering all these factors, this invention controls the holding and tapping temperatures of the continuously cast billet to be between 1160℃ and 1180℃.

[0081] If the holding time of the continuously cast billet in the 1160℃-1180℃ temperature range is less than 45 minutes and the cumulative furnace dwell time is less than 180 minutes, its microstructure is not easily homogenized, rolling energy consumption is high, and equipment accidents are prone to occur. If the holding time of the continuously cast billet in the 1160℃-1180℃ temperature range is longer than 52.5 minutes and the cumulative furnace dwell time is longer than 210 minutes, oxidation loss, decarburization, and energy consumption increase, while the mill operating rate and production efficiency decrease. Therefore, taking all the above effects into consideration, this invention controls the holding time of the continuously cast billet in the 1160℃-1180℃ temperature range to be 45-52.5 minutes, the billet exiting the furnace at 1160℃-1180℃, and the cumulative furnace dwell time to be 180-210 minutes.

[0082] In S3, the continuously cast billet is rough rolled in 7 passes, and the rough rolling start temperature is controlled at 1110℃-1130℃ and the rough rolling finish temperature is controlled at 1040℃-1080℃.

[0083] Practice has shown that the main metallurgical purpose of rough rolling is to disrupt the as-cast structure of the continuously cast billet, effectively refine the austenite grains through multiple recrystallizations, and obtain a uniform and fine austenite structure. If the rough rolling start temperature is too high, austenite grain inhomogeneity will occur, leading to differences in the strip structure and affecting the uniformity of the finished product's mechanical properties. If the rough rolling start temperature is too low, the difficulty of controlling the strip shape increases, the mill load and rolling energy consumption rise, which is not conducive to smooth rolling. Therefore, considering the above effects, this invention controls the rough rolling start temperature to 1110℃-1130℃ and the rough rolling finish temperature to 1040℃-1080℃.

[0084] In S4, the strip is finished rolled using a 7-stand finishing mill, with the initial finishing temperature controlled at 980℃-1030℃, the final finishing temperature at 830℃-870℃, and the hot-rolled strip thickness at 4.0-6.0mm.

[0085] Practice has shown that if the finishing rolling start temperature is too high, partial recrystallization can easily occur in the F1 and F2 finishing mill stands, leading to mixed crystal problems, differences in the microstructure of the finished steel strip, and abnormal fluctuations in mechanical properties. If the finishing rolling start temperature is too low, the desired final rolling temperature cannot be guaranteed. Therefore, taking all the above factors into consideration, this invention controls the finishing rolling start temperature to 980℃-1030℃.

[0086] Practice has shown that if the finishing rolling temperature is too high, the finished steel strip will have a coarsened microstructure and reduced strength and toughness. If the finishing rolling temperature is too low, the finished steel strip will have increased strength but decreased plasticity, resulting in an unreasonable strength-plasticity balance. This also reduces the rolling stability of the finishing mill, making it more difficult to control the thickness, width, and cross-sectional shape of the steel strip. In severe cases, it can lead to scrapped steel strip and equipment damage. Taking all these factors into consideration, this invention controls the finishing rolling temperature to 830℃-870℃.

[0087] In S5, the cooling method of hot-rolled steel strip on the laminar flow cooling roller table is front-end densified laminar flow cooling, and the flow ratio of cooling water in the upper and lower manifolds is controlled at 10:12.

[0088] Practice has shown that, compared with other cooling methods, front-end densified laminar flow cooling is beneficial for refining ferrite grains, resulting in a good balance of strength, toughness, plasticity, and cold forming properties in the finished steel strip. Therefore, taking all the above factors into consideration, the cooling method for hot-rolled steel strip on the laminar flow cooling roller table in this invention adopts front-end densified laminar flow cooling.

[0089] Practice has shown that if the cooling water flow ratio of the upper and lower manifolds is higher or lower than 10:12, it will cause a large difference in the cooling rate of the upper and lower surfaces of the steel strip, resulting in fluctuations in the microstructure and mechanical properties, and will also increase the difficulty of plate shape control. Therefore, taking into account the above factors, the present invention controls the cooling water flow ratio of the upper and lower manifolds to be 10:12.

[0090] In S6, the hot-rolled steel strip coiling temperature is controlled at 550℃-590℃ during the hot-rolled steel strip coiling process.

[0091] Practice has shown that by properly controlling the coiling temperature, the γ→α phase transformation temperature can be appropriately reduced, increasing the α phase nucleation rate, refining ferrite grains, and simultaneously increasing the proportion of bainite in the microstructure. Bainite grains are finer than ferrite grains, approximately 1 μm in size, and have a higher dislocation density, thus improving the overall mechanical properties of the steel strip. Furthermore, properly controlling the coiling temperature is also a necessary measure to reduce the difficulty of controlling the strip shape and coil shape. Taking all these factors into consideration, the present invention controls the coiling temperature to be 550℃-590℃.

[0092] To more clearly demonstrate the performance comparison between this embodiment and Comparative Example 1 (CN202211337425.2), Comparative Example 2 (CN202410138488), and Comparative Example 3 (CN202210677545.0), specific parameter comparisons are shown in Tables 1-4:

[0093] Table 1. Comparison of chemical composition (mass percentage) of the embodiments and comparative examples of the present invention.

[0094]

[0095] Table 2 Comparison of furnace loading and heating process parameters between the embodiments and comparative examples of the present invention.

[0096]

[0097] Table 3 Comparison of rolling and cooling process parameters between the embodiments and comparative examples of the present invention

[0098]

[0099] Table 4 Performance Comparison of Embodiments and Comparative Examples of the Invention

[0100]

[0101] As shown in Tables 1-4, the chemical composition, furnace loading, heating, rough rolling, finish rolling, cooling and other process parameters of the embodiments of the present invention are significantly different from those of the comparative examples, and the various properties are also significantly different. The low alloy corrosion-resistant steel in the present invention can better meet the new requirements for the development of photovoltaic brackets, such as high strength and toughness, lightweight, high corrosion resistance, long service life, easy manufacturing, low cost, high efficiency, no painting required, no maintenance, energy saving and environmental protection.

[0102] As can be seen from the above process, the low-alloy corrosion-resistant steel and its manufacturing method in this invention optimize the design of the content of elements such as C, Si, Mn, P, S, Cu, Cr, Ti, Alt, T[O], N, and B, and control the Ti / N ratio, continuous casting billet charging temperature, heating time in different temperature ranges, furnace exit temperature, furnace dwell time, rough rolling start and finish rolling temperatures, finish rolling start and finish rolling temperatures, rolling passes, finished product thickness, cooling method, cooling water flow ratio of upper and lower manifolds, and coiling temperature, so that the finished steel has a grain size of grade 11 or above, yield strength ≥750MPa, tensile strength ≥850MPa, elongation after fracture ≥18%, strength-ductility product ≥15.3 (GPa·%), passes the 180°d=a cold bending test, impact absorption energy at -40℃ ≥120J, and Brinell hardness ≥245. After 72 hours of cyclic immersion in a NaHSO3 solution with an initial concentration of 0.01 mol / L, the corrosion rate relative to Q355B ordinary steel is ≤28%.

[0103] The low-alloy corrosion-resistant steel of this invention has low content of harmful and impurity elements, is pure in quality, and has high strength and toughness. Replacing Q235B galvanized steel can reduce weight by 36%, resulting in significant weight reduction. This low-alloy corrosion-resistant steel also exhibits strong corrosion resistance and excellent formability, meeting the stringent processing and service requirements of photovoltaic brackets.

[0104] Meanwhile, the low-alloy corrosion-resistant steel has moderate P and Al content, low Cu and Ti content, and no low-boiling-point element Mg, which avoids its adverse effects on plasticity, toughness, weldability, surface quality, etc., making the mechanical properties more stable and easier to smelt, continuously cast and control plate and coil shape, thereby improving the production efficiency of steel and photovoltaic brackets.

[0105] Furthermore, this low-alloy corrosion-resistant steel does not contain precious alloying elements such as W, Ni, Nb, V, and Mo, and has a low Mn content, effectively reducing alloy production costs. At the same time, photovoltaic brackets made from this low-alloy corrosion-resistant steel require no subsequent pickling, painting, or maintenance, offering advantages such as energy saving, environmental friendliness, short delivery cycles, and low operating costs.

[0106] It should be noted that, unless otherwise stated, the technical or scientific terms used in this invention should have the ordinary meaning as understood by one of ordinary skill in the art.

[0107] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention 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 high-strength, high-toughness, low-alloy corrosion-resistant steel for photovoltaic brackets, characterized in that, The composition of the high-strength, high-toughness, low-alloy corrosion-resistant steel by mass percentage includes: C: 0.17%-0.20%, Si: 0.80%-0.95%, Mn: 0.10%-0.19%, P: 0.031%-0.039%, S: 0.0020%-0.0030%, Cu: 0.13%-0.18%, Cr: 3.1%-3.3%, Ti: 0.010%-0.025%, Alt: 0.02%-0.06%, T[O]: 0.0010%-0.0020%, N: 0.0030%-0.0055%, B: 0.0021%-0.0031%, with the remainder being Fe and unavoidable impurities; The high-strength, high-toughness, low-alloy corrosion-resistant steel shall satisfy Ti / N≥3.4; The high-strength, high-toughness, low-alloy corrosion-resistant steel has the following properties: Grain size ≥ 11; Yield strength ≥750MPa, tensile strength ≥850MPa, elongation after fracture ≥18%, strength-ductility product ≥15.3 (GPa·%), qualified for 180°d=a cold bending test, impact energy absorbed at -40℃ ≥120J, Brinell hardness ≥245; After 72 hours of cyclic immersion in a NaHSO3 solution with an initial concentration of 0.01 mol / L, the corrosion rate relative to Q355B ordinary steel is ≤28%. The manufacturing method of high-strength, high-toughness, low-alloy corrosion-resistant steel includes the following steps: S1, through hot metal pretreatment desulfurization, top and bottom combined blowing converter smelting, LF refining, RH refining and slab continuous casting, to obtain a continuously cast billet with a thickness of 180-230mm; S2, the continuously cast billet is heated and loaded into a walking beam furnace for heating and heat preservation; S3 uses a roughing mill to roll the continuously cast billet to obtain a strip billet; S4 uses a finishing mill to roll the strip billet to obtain hot-rolled steel strip; S5, hot-rolled steel strip is cooled during transport on a laminar flow cooling roller conveyor; S6, hot-rolled steel strip is wound into hot-rolled steel coil by a coiler; In S2, the heating time of the continuously cast billet in the temperature range of 550℃-700℃ is controlled to be 60-67.5 minutes, the heating time in the temperature range of 700℃ to 1170±10℃ is controlled to be 75-90 minutes, and the holding time in the temperature range of 1160℃-1180℃ is controlled to be 45-52.5 minutes. The billet exit temperature is controlled to be 1160℃-1180℃, and the cumulative furnace dwell time is controlled to be 180-210 minutes. In S4, the strip is finished rolled using a 7-stand finishing mill, with the initial finishing temperature controlled at 980℃-1030℃, the final finishing temperature at 830℃-870℃, and the hot-rolled strip thickness at 4.0-6.0mm. In S5, the cooling method of hot-rolled steel strip on the laminar flow cooling roller table is front-end intensified laminar flow cooling, and the flow ratio of cooling water in the upper and lower manifolds is controlled at 10:

12.

2. The method for manufacturing high-strength, high-toughness, low-alloy corrosion-resistant steel according to claim 1, characterized in that, In S2, the continuous casting billet charging temperature is controlled to be ≥550℃, and the time from billet discharge to loading into the walking beam furnace is controlled to be ≤8 hours.

3. The method for manufacturing high-strength, high-toughness, low-alloy corrosion-resistant steel according to claim 1, characterized in that, In S3, the continuously cast billet is rough rolled in 7 passes, and the rough rolling start temperature is controlled at 1110℃-1130℃ and the rough rolling finish temperature is controlled at 1040℃-1080℃.

4. The method for manufacturing high-strength, high-toughness, low-alloy corrosion-resistant steel according to claim 1, characterized in that, In S6, the hot-rolled steel strip coiling temperature is controlled at 550℃-590℃ during the hot-rolled steel strip coiling process.

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