Weather-proof steel plate with yield strength of 345 MPa for rare earth La photovoltaic support and preparation method of weather-proof steel plate

Abstract

The invention relates to a weather-resistant steel plate for a rare earth La photovoltaic support with yield strength of 345 MPa and a preparation method, belongs to the technical field of weather-resistant steel, and solves the problem that traditional weather-resistant steel lacks price advantage in market competition with hot-dip galvanized steel due to high alloy content and high initial cost. The weather-resistant steel plate for the rare earth La photovoltaic support with the yield strength of 345 MPa comprises the following components in percentage by mass: 0.12%-0.15% of C, 0.20%-0.40% of Si, 0.30%-0.50% of Mn, less than or equal to 0.018% of P, less than or equal to 0.0028% of S, less than or equal to 0.0032% of O, 0.0052%-0.0350% of La, 0.13%-0.25% of Cu, 0.48%-0.90% of Cr, 0.022%-0.050% of Nb and the balance of Fe and inevitable impurities. The steel plate has the advantages of being low in cost, excellent in corrosion resistance and good in obdurability, economical efficiency and high performance of the steel for the photovoltaic support are both achieved, and the requirements for low cost, high corrosion resistance and high strength of weather-resistant steel in the photovoltaic field of C1 and C2 low-corrosion areas in the northwest are met.

Description

Technical Field

[0001] The present invention relates to the technical field of weathering steel, and in particular to a weathering steel plate for a rare earth La photovoltaic support with a yield strength of 345 MPa and a preparation method thereof. Background Art

[0002] Weathering steel, due to its excellent corrosion resistance, has become a potential alternative material. It can be used exposed to atmospheric conditions without the need for surface coating, thus reducing maintenance costs and environmental pollution. However, due to the high alloy content and high initial cost of traditional weathering steel, this high initial cost cannot be offset by maintenance savings, and it still lacks a price advantage in the market competition with hot-dip galvanized steel.

[0003] Therefore, the development of a weathering steel that has excellent corrosion resistance and meets the mechanical performance requirements of photovoltaic brackets while significantly reducing the initial cost is of great significance to the sustainable development of the photovoltaic industry in the C1 and C2 low-corrosion areas in the northwest. Summary of the Invention

[0004] In view of the above analysis, the embodiments of the present invention aim to provide a weathering steel plate and preparation method for rare earth La photovoltaic brackets with a yield strength of 345 MPa, so as to solve the problem that traditional weathering steel lacks price advantage in market competition with hot-dip galvanized steel due to its high alloy content and high initial cost.

[0005] On the one hand, an embodiment of the present invention provides a weathering steel plate for rare earth La photovoltaic bracket with a yield strength of 345 MPa. The components of the weathering steel plate for rare earth La photovoltaic bracket with a yield strength of 345 MPa include, by mass percentage: C: 0.12%~0.15%, Si: 0.20%~0.40%, Mn: 0.30%~0.50%, P: ≤0.018%, S: ≤0.0028%, O: ≤0.0032%, La: 0.0052%~0.0350%, Cu: 0.13%~0.25%, Cr: 0.48%~0.90%, Nb: 0.022%~0.050%, and the balance is Fe and unavoidable impurities.

[0006] Furthermore, the components of the weathering steel plate for rare earth La photovoltaic bracket with a yield strength of 345MPa include, in mass percentage, C: 0.12%~0.15%, Si: 0.20%~0.40%, Mn: 0.30%~0.50%, P: ≤0.010%, S: ≤0.0028%, O: ≤0.0032%, La: 0.0052%~0.0250%, Cu: 0.13%~0.25%, Cr: 0.60%~0.90%, Nb: 0.030%~0.040%, and the balance is Fe and unavoidable impurities.

[0007] Furthermore, the thickness of the weathering steel plate with a yield strength of 345 MPa grade rare earth La for photovoltaic support is 1.5 to 12 mm.

[0008] Furthermore, the microstructure of the weathering steel plate with a yield strength of 345 MPa grade rare earth La for photovoltaic brackets is ferrite, pearlite and bainite.

[0009] Furthermore, the yield strength 345MPa grade rare earth La weathering steel plate for photovoltaic bracket was subjected to a 72-hour immersion accelerated corrosion test according to TB / T 2375-93 standard, and the corrosion rate was 1.8-2.2g / m 2 ·h.

[0010] Furthermore, the yield strength of the 345MPa grade rare earth La weathering steel plate for photovoltaic brackets has a yield strength of ≥395MPa, a tensile strength of ≥530MPa, and an elongation A of ≥26%.

[0011] Furthermore, the 0°C impact energy KV2 of the 345MPa yield strength rare earth La weathering steel plate for photovoltaic support is ≥115J.

[0012] On the other hand, an embodiment of the present invention provides a method for preparing a weathering steel plate with a yield strength of 345 MPa for rare earth La photovoltaic supports. The method is used to prepare the above-mentioned weathering steel plate with a yield strength of 345 MPa for rare earth La photovoltaic supports, comprising the following steps:

[0013] S1: molten iron pretreatment;

[0014] S2: converter smelting;

[0015] S3: LF refining;

[0016] S4: continuous casting to obtain ingot;

[0017] S5. The ingot is heated to 1190-1210° C. and kept warm for 1.5-2.5 hours, and then hot-rolled. The ingot is then controlled cooled, coiled, and flattened to obtain a weathering steel plate with a yield strength of 345 MPa grade rare earth La for photovoltaic supports.

[0018] Furthermore, in S1, the KR method is used for pre-desulfurization treatment, the desulfurizer is a CaO+CaF2 mixture, and the sulfur content of the molten iron is controlled at ≤50ppm; in S3, white slag desulfurization is performed, the slag basicity is 5.5-6.5, the sulfur content of the molten steel after refining is ≤30ppm, the oxygen content is ≤30ppm, and lanthanum iron alloy is added to achieve precise micro-alloying of La.

[0019] Furthermore, in S5, the starting rolling temperature of the hot rolling is 1020-1080°C, and the finishing rolling temperature is 860-875°C; controlled cooling includes: first water cooling the hot-rolled steel billet to 580-620°C at a cooling rate of 10-30°C / s, and then air cooling to room temperature.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1) The weathering steel sheet of this invention completely replaces the traditional expensive Ni by adding La, and reduces the Cu content, while avoiding the segregation problem caused by high Cu content and reducing subsequent processing costs. The total alloy cost is 22% lower than that of traditional weathering steel and 15% lower than the full life cycle cost of hot-dip galvanized steel.

[0022] 2) The Ni-free weathering steel of the present invention was subjected to a 72-hour immersion accelerated corrosion test according to TB / T 2375-93 standard, and the corrosion rate was 1.8-2.2 g / m 2 h, meeting the TB / T 2375-93 weathering steel standard. In the low-corrosion environment of western China, weathering steel sheets can be used bare without galvanizing, reducing zinc consumption by 3.5 kg per ton of steel. This not only effectively lowers overall lifecycle costs but also reduces environmental pollution during the galvanizing process. Compared to traditional hot-dip galvanized photovoltaic racks, this product offers less environmental pollution and greater market competitiveness.

[0023] 3) The present invention breaks through the system limitations of traditional weathering steel and constructs a Cu-La-Cr ternary corrosion-resistant system for the first time. Among them, 0.13%-0.25% Cu, 0.0052%-0.0350% La and 0.48%-0.90% Cr work synergistically through the triple mechanism of "rust layer modification-electrochemical corrosion inhibition-matrix strengthening", significantly improving the density of the rust layer and reducing the corrosion rate under the C2 environment. Specifically, Cu promotes the formation of α-FeOOH rust layer, La acts as a corrosion inhibitor to slow down corrosion, and Cr increases the corrosion potential of the matrix. This Ni-free weathering steel achieves an optimized balance between performance and cost, filling the gap in the design of weathering steel composition.

[0024] 4) In traditional weathering steel, rare earth elements are often added in the form of mixed rare earths or multiple rare earth elements (such as La and Ce). However, through comparative tests, the present invention found that La has better corrosion resistance than Ce in weathering steel sheets for photovoltaic brackets. Therefore, the present invention chooses to add La alone and control its content to 0.0052%-0.0350%. In addition, by controlling the oxygen content, this not only avoids large amounts of La2O3 inclusions, but also significantly reduces the corrosion rate, thereby improving corrosion resistance.

[0025] 5) This weathering steel combines excellent corrosion resistance with mechanical properties. Its yield strength exceeds 395 MPa, its tensile strength exceeds 530 MPa, and its elongation exceeds 26%, ensuring structural stability when supporting photovoltaic equipment. It also performs exceptionally well in low-temperature environments, achieving an impact energy KV2 exceeding 115 J at 0°C. It effectively withstands impact loads in cold regions, laying a solid foundation for the safe operation of photovoltaic mounts in all climates.

[0026] 6) The weathering steel production process of the present invention relies on a mature process involving hot metal pretreatment, converter smelting, LF refining, continuous casting, and hot rolling. The operating parameters of each step are clearly defined, resulting in a stable and efficient production process. Because it utilizes common, established technologies, it requires no additional professional training and is suitable for large-scale industrial production, further enhancing its market competitiveness.

[0027] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0029] Figure 1 This is a typical microstructure diagram of the weathering steel plate of the present invention. DETAILED DESCRIPTION

[0030] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0031] Traditional weathering steel lacks cost competitiveness in photovoltaic bracket applications, primarily due to its specialized alloy composition requirements. This type of steel requires the addition of precious metals such as Cu, Cr, and Ni (approximately 2% to 3% in total), resulting in raw material costs 25% to 35% higher than those of ordinary carbon steel. Cost reduction typically involves three major technical bottlenecks: First, alloy substitution can reduce performance. For example, replacing Cr with Al can compromise the density of the rust layer, thereby reducing corrosion resistance. Second, process limitations. For example, high Cu content can lead to segregation, requiring the addition of Ni or specialized processes (such as electromagnetic stirring) to address this issue, increasing production costs. Third, performance balance issues arise. For example, when the Cr content exceeds 1%, the material's welding performance becomes difficult to control.

[0032] In order to solve the above problems, the present invention has developed a low-cost weathering steel suitable for the western C1 and C2 low-corrosion environments. The western C1 and C2 low-corrosion environments are characterized by relatively low concentrations of corrosive media and relatively mild climatic conditions. The requirement for weathering steel is to reduce production costs while ensuring certain corrosion resistance. The present invention significantly improves the atmospheric corrosion resistance of steel by adding the rare earth element La, and completely replaces the more expensive Ni in traditional weathering steel, while reducing the content of the alloying element Cu. These improvements not only ensure that the corrosion resistance of the steel meets national standards, but also avoid the segregation problem caused by high Cu content, reducing subsequent process costs. Ultimately, the total cost of the alloy is 22% lower than that of traditional weathering steel and 15% lower than the full life cycle cost of hot-dip galvanized steel.

[0033] On the one hand, a specific embodiment of the present invention discloses a weathering steel plate for a photovoltaic bracket with a yield strength of 345 MPa grade rare earth La. The components of the weathering steel plate include, by mass percentage: C: 0.12%~0.15%, Si: 0.20%~0.40%, Mn: 0.30%~0.50%, P: ≤0.018%, S: ≤0.0028%, O: ≤0.0032%, La: 0.0052%~0.0350%, Cu: 0.13%~0.25%, Cr: 0.48%~0.90%, Nb: 0.022%~0.050%, and the balance is Fe and unavoidable impurities.

[0034] The present invention breaks through the system limitations of traditional weathering steel and constructs a Cu-La-Cr ternary corrosion-resistant system for the first time. Among them, 0.13%-0.25% Cu, 0.0052%-0.035% La and 0.48%-0.90% Cr work synergistically through the triple mechanism of "rust layer modification-electrochemical corrosion inhibition-matrix strengthening", significantly improving the density of the rust layer and reducing the corrosion rate under the C2 environment. Specifically, Cu promotes the formation of α-FeOOH rust layer, La acts as a corrosion inhibitor to slow down corrosion, and Cr increases the corrosion potential of the matrix. This Ni-free weathering steel achieves an optimal balance between performance and cost, filling the gap in the design of weathering steel composition.

[0035] The following is a detailed description of the effects and dosage of the components in the present invention:

[0036] C: Although the addition of carbon can significantly improve the hardness and strength of steel, too much carbon will reduce the plasticity and toughness of steel. Within the composition range of conventional weathering steel, the effect of carbon on weathering resistance is very small. Therefore, the present invention comprehensively considers the synergistic relationship between the strength and toughness of the material. When the carbon content is within a specific range, it can cooperate with other elements to improve the strength while ensuring a certain plasticity and toughness. After a large number of experiments and theoretical analysis, its content is controlled to be 0.12% to 0.15%, for example, 0.12%, 0.13%, 0.14%, and 0.15%. Compared with the prior art, this content range not only meets the strength requirements of photovoltaic brackets, but also avoids excessive loss of toughness due to excessive carbon content.

[0037] Si: Silicon can increase the quenching, normalizing and annealing temperatures of steel, and improve the tempering stability and oxidation resistance of steel. Silicon can be dissolved in ferrite and austenite, synergistically improving the strength, hardness, elasticity and wear resistance of steel. However, excessive Si addition will deteriorate the welding performance of steel. This is because excessive silicon will change the microstructure of the weld metal, affect its crystallization process, and thus weaken the performance of the weld joint. The present invention fully considers the interaction between silicon and elements related to welding performance, such as manganese, and controls its content to 0.20% to 0.40%, for example, 0.20%, 0.22%, 0.25%, 0.30%, 0.35%, 0.38% or 0.40%, so that silicon can play its advantages of strengthening and anti-oxidation while maintaining the welding performance within an acceptable range. This content design is an optimized choice after comprehensive consideration of multiple performance requirements and combined with synergistic effects with other elements, which is different from some existing technologies that simply focus on the silicon content setting of a certain performance.

[0038] Mn: Manganese can improve the hardenability of steel and has a significant effect on improving the strength of ordinary low-alloy steel. When the manganese content is too high, the welding performance of the steel will deteriorate, promote grain growth, and reduce the toughness of the weld metal. This is because manganese can reduce the critical cooling rate of steel, promote grain refinement, and thus strengthen the matrix. However, when the manganese content is too high, it will produce a bad synergy with impurity elements such as sulfur in the steel, causing abnormal grain growth, which not only reduces the toughness of the weld metal, but also affects the uniformity of the overall mechanical properties. Within the conventional range of weathering steel components, manganese has little effect on weathering resistance. Therefore, the present invention mainly considers the effect of manganese on strength and welding performance. The present invention comprehensively considers the interaction between manganese and elements such as carbon and silicon in the strengthening mechanism and the welding process. For example, the appropriate combination of manganese and silicon can adjust the solidification mode of the weld metal and improve welding performance; it works together with carbon to improve hardenability and accurately control the structural transformation. After repeated testing, the manganese content was determined to be controlled between 0.30% and 0.50%, for example, 0.30%, 0.33%, 0.36%, 0.40%, 0.45%, 0.48%, or 0.50%. This range not only fully utilizes manganese's strength-enhancing benefits, but also, through synergy with other elements, suppresses its negative impact on weldability. This differs from existing manganese content designs that focus solely on strength improvement while ignoring weldability degradation.

[0039] Phosphorus (P): Phosphorus can significantly reduce the plasticity and toughness of steel, particularly at low temperatures. This phenomenon, known as cold brittleness, is due to phosphorus segregation at grain boundaries, reducing their bonding strength. Phosphorus also interacts with other alloying elements in steel, further reducing the material's weldability. For example, phosphorus combines with manganese to form brittle phases, deteriorating weld quality. However, phosphorus has a unique promoting effect on atmospheric corrosion, altering the structure and composition of the rust layer and improving its protective properties. The present invention comprehensively considers the conflicting relationship between the material's mechanical properties and corrosion resistance, as well as the synergistic effects of phosphorus with other elements during corrosion. Through precise regulation, phosphorus content is controlled to ≤ 0.018%, for example, 0.010%, 0.012%, 0.015%, 0.017%, or 0.018%. This ensures that while utilizing phosphorus's corrosion resistance benefits, its detrimental effects on mechanical properties, particularly toughness and weldability, are minimized. This contrasts with some existing techniques that simply limit phosphorus content without fully considering the impact of phosphorus and multiple elements on the overall performance.

[0040] S: Sulfur exists mainly in the form of sulfide in steel. It forms low-melting-point eutectic compounds with elements such as iron and manganese, which are distributed at grain boundaries, greatly reducing the strength, elongation and impact value of steel, while destroying the density of the rust layer and reducing the corrosion resistance of steel. The present invention is well aware of the comprehensive negative impact of sulfur on the performance of steel. When considering the balance between desulfurization cost and performance improvement, it fully combines the inhibition or conversion effect of other elements (such as rare earth La, etc., and the synergistic purification effect of La and sulfur will be described later) on sulfur, and controls its content as low as possible. Considering that too low sulfur content requires a certain desulfurization cost, the present invention controls its content to ≤0.0028%, such as 0.0010%, 0.0015%, 0.0020%, 0.0025% or 0.0028%. This content control is an optimized decision after comprehensive multi-element synergistic desulfurization and cost-effectiveness. It is more reasonable than the existing technology that partially ignores the synergistic purification mechanism of sulfur and other elements, does not completely remove sulfur, or excessively pursues low sulfur costs.

[0041] O: Oxygen exists in steel mainly in the form of oxides. Various oxides will become stress concentration sources, reducing the mechanical properties of steel. On the other hand, they will destroy the integrity and density of the rust layer, which is not conducive to improving corrosion resistance. Therefore, it is necessary to strictly control the oxygen content to the lowest possible level. At the same time, oxygen and rare earth La form La2O3, which has stable chemical properties and will not dissolve during the corrosion process, and cannot form La 3+ ions, thereby suppressing the effect of this rare earth La on the corrosion resistance of the material. While considering the cost of deoxidation, the present invention takes into account the special interaction between oxygen and rare earth La and its impact on overall corrosion resistance. By optimizing the steelmaking process and coordinating with other elements, its content is controlled to ≤ 0.0032%, for example, 0.0010%, 0.0015%, 0.0020%, 0.0026%, 0.0030% and 0.0032%, ensuring that the adverse effects of oxygen on the overall performance of the material are minimized to the greatest extent possible under the premise of economic feasibility. This oxygen content control strategy based on multi-element synergy is different from some existing technologies that do not deeply consider the mutual restriction relationship between oxygen and rare earth elements.

[0042] La is a key element used in this invention to improve the corrosion resistance of weathering steel. The addition of rare earth La significantly optimizes the steel's microstructure and properties, refining its grain structure while also increasing its strength and toughness. Furthermore, the addition of La improves the steel's corrosion resistance and weldability, providing superior overall performance for applications such as photovoltaic brackets.

[0043] As a key alloying element, La forms a synergistic corrosion-resistant system with Cu and Cr: La refines grains and improves the rust layer structure, and together with Cu promotes the formation of a dense α-FeOOH protective layer. At the same time, Cr improves the matrix passivation ability. The three elements double the corrosion resistance through the "La-Cu composite oxide formation" and "Cr-La synergistic passivation" mechanisms.

[0044] Specifically, La exists in steel in the form of solid-solution metal lanthanum, metal lanthanum / iron metal compounds, lanthanum oxide, lanthanum oxysulfide, and lanthanum sulfide. In the corrosive medium, these compounds do not play a role in isolation, but rather work in synergy with each other. Among them, solid-solution metal lanthanum and metal lanthanum / iron metal compounds are the main active components, which preferentially dissolve in the early stage of corrosion and release La3 + ions, and La 3+ The ions act as anodic corrosion inhibitors in industrial and rural atmospheric corrosion environments, adsorbing onto metal surfaces to inhibit anodic reactions and slow atmospheric corrosion. Furthermore, sulfur-containing compounds such as lanthanum sulfide can bind to sulfur impurities in steel, reducing the negative impact of sulfur on corrosion resistance.

[0045] To optimize the presence and content of lanthanum in steel, the present invention precisely controls the oxygen content (≤30ppm) and sulfur content (≤30ppm) in the steel, regulating the distribution of lanthanum in its chemical state, so that the effective lanthanum content in the form of solid-solution rare earth lanthanum and rare earth lanthanum / intermetallic compounds in the steel reaches 65%-85%. The effective lanthanum content in the steel is calculated using the following formula: Effective lanthanum content in steel = solid-solution metal lanthanum content + metal lanthanum / iron metal compound content + 0.3 × lanthanum sulfide content. This measure ensures that the effective rare earth lanthanum content is not less than 70% (e.g., 70%-87%), thereby fully utilizing the effective rare earth lanthanum to improve corrosion resistance.

[0046] The outstanding innovation of the present invention is to replace the high-cost Ni by adding rare earth La. This substitution is not a simple element replacement, but is based on the unique synergistic corrosion resistance mechanism of La and other elements to achieve performance equivalent to or even surpass. At the same time, in order to avoid the formation of a large amount of metal lanthanum / iron metal compounds in steel due to excessive La content, the present invention controls the La content to 0.0052% to 0.0350%, such as 0.0052%, 0.0080%, 0.0100%, 0.0150%, 0.0200%, 0.0250%, 0.0300% and 0.0350%. This content design is the result of multi-factor synergistic optimization that takes into account corrosion resistance, toughness and cost, and is significantly different from the existing technology that relies on the traditional nickel-based corrosion resistance system or does not precisely control the lanthanum content.

[0047] It should be noted that the addition of rare earth elements in traditional weathering steel usually appears in the form of mixed rare earths, or multiple rare earth elements (such as La and Ce) are added at the same time. However, after a large number of comparative tests, the present invention found that in the application scenario of weathering steel plates for photovoltaic brackets, compared with rare earth Ce, rare earth La has a better synergistic effect with other elements in steel in terms of resistance to industrial atmospheric corrosion and resistance to rural atmospheric corrosion. For example, the synergistic effect of La with corrosion-resistant elements such as copper and chromium in the formation and stabilization of the rust layer is stronger than Ce, and can more efficiently promote the formation of a dense weathering rust layer. Therefore, the present invention chooses to add rare earth La alone and control its content to 0.0052%-0.035%. This not only avoids La2O3 inclusions, but also significantly reduces the corrosion rate. This is the key difference between the present invention and the prior art in rare earth application strategy.

[0048] Cu: Copper is a key element in improving the corrosion resistance of weathering steel. It works synergistically with elements like iron and oxygen in the steel to promote the formation of an α-FeOOH rust layer. α-FeOOH is the primary component of this dense, weathering-resistant rust layer, effectively preventing further intrusion of corrosive media into the substrate and providing excellent protection. Especially in humid and acidic environments, copper helps form a dense oxide film, further enhancing the steel's resistance to atmospheric corrosion.

[0049] However, copper is expensive, and when its content is high (e.g., 0.25%-0.5%), it is prone to segregation with other elements during solidification, changing the local microstructure and properties, resulting in uneven material properties. This requires adding an appropriate amount of nickel or employing special processes (such as electromagnetic stirring), which undoubtedly significantly increases production costs.

[0050] Therefore, the present invention takes into full consideration the synergistic effect of copper with other corrosion-resistant and strengthening elements (such as chromium, lanthanum, etc.) from the perspective of comprehensive balance between cost and performance. Under the premise of ensuring the protective performance of the rust layer, the use of copper is reduced and its content is controlled at 0.13%-0.25%. For example, the copper content can be 0.13%, 0.15%, 0.18%, 0.20%, 0.22%, 0.24% and 0.25%. This content range can not only maintain the key role of copper in the construction of weather-resistant rust layer, but also avoid the cost and quality problems caused by excessive copper through synergistic optimization with multiple elements. Compared with some existing technologies that do not finely control the copper content, the present invention has more advantages.

[0051] Chromium (Cr): Chromium is a key element in improving the corrosion resistance of weathering steel. It not only increases the hardness and strength of the steel plate, but also enhances its oxidation and corrosion resistance, enabling it to maintain stable performance in high temperatures and harsh environments, meeting the long-term performance requirements of photovoltaic mounts. Chromium can be integrated into the steel matrix, increasing its corrosion potential and slowing down corrosion. Furthermore, chromium synergizes with oxygen, iron, and other elements in the steel to promote the formation of an α-FeOOH rust layer, making the rust layer denser and further enhancing corrosion resistance.

[0052] However, too high a chromium content will form complex carbides with elements such as carbon in the steel. These carbides gather at the grain boundaries, which will reduce the toughness and welding performance of the material. The Cr content in traditional weathering steel is generally 0.40%-1.5%. However, in actual production, considering comprehensive factors such as cost and performance, the chromium content is usually controlled between 0.40%-1.0%. Based on an in-depth study of the synergistic effect of chromium and other elements (such as Cu, La, etc.), the present invention comprehensively considers mechanical properties, corrosion resistance and cost, and controls the chromium content to 0.48%-0.90%. For example, the chromium content can be 0.48%, 0.55%, 0.62%, 0.70%, 0.80% and 0.90%. This content design is based on an in-depth study of the synergistic effect of chromium and multi-element alloy systems, taking into account the optimization selection of various performances, which is different from the traditional technology that only controls the chromium content based on experience or a single performance focus.

[0053] Nb: Niobium is primarily used during the controlled rolling and controlled cooling process to synergize with elements like carbon and nitrogen in steel, affecting the microstructure and achieving desired mechanical properties through mechanisms like grain refinement and phase transformation control. For example, the carbides formed by niobium and carbon can pin grain boundaries during high-temperature rolling, inhibiting grain growth and improving strength and toughness. While it has little impact on corrosion resistance, it works in conjunction with other elements that influence corrosion resistance and mechanical properties within the overall material performance optimization system to ensure that corrosion resistance requirements are met while achieving a good balance of mechanical properties. The present invention controls its content within a range of 0.022% to 0.050%, for example, 0.022%, 0.030%, 0.038%, 0.040%, 0.045%, and 0.050%. This content range is determined based on the synergistic effects of niobium and the multi-element alloy system during controlled rolling and controlled cooling, combined with the mechanical property requirements of the final product. This distinguishes it from existing technologies that fail to fully consider the synergistic controlled rolling and controlled cooling effects of niobium and multiple elements.

[0054] In order to further improve the comprehensive performance of the above-mentioned 345MPa yield strength rare earth La weathering steel plate for photovoltaic brackets, its components can be further optimized.

[0055] In one embodiment, the components of the weathering steel plate described above include, in mass percentage: C: 0.12%~0.15%, Si: 0.20%~0.40%, Mn: 0.30%~0.50%, P: ≤0.010%, S: ≤0.0028%, O: ≤0.0032%, La: 0.0052%~0.0250%, Cu: 0.13%~0.25%, Cr: 0.60%~0.90%, Nb: 0.030%~0.040%, and the balance of Fe and inevitable impurities.

[0056] By reducing the upper limit of phosphorus content from 0.018% to 0.010%, the negative impact of phosphorus on the cold brittleness and welding performance of the steel is further reduced, while still retaining a little contribution of phosphorus to corrosion resistance. At the same time, the upper limit of lanthanum content is controlled at 0.0250%, which ensures the corrosion resistance while avoiding the decrease of toughness of the steel caused by excessive lanthanum content. Finally, the niobium content is controlled at 0.030%-0.040%, which better controls the microstructure during controlled rolling and controlled cooling, thereby obtaining more ideal mechanical properties. Through these optimizations, the weathering steel plate of this embodiment further improves the toughness and welding performance of the material while maintaining good corrosion resistance, and is particularly suitable for application scenarios that require high toughness and good welding performance, such as complex structure connection parts of photovoltaic support.

[0057] Further, the yield strength 345 MPa grade rare earth La weathering steel plate for photovoltaic support has a thickness of 1.5-12 mm. The 1.5-3.0 mm thin plate is particularly suitable for light structures such as distributed photovoltaic systems and roof photovoltaic supports, which significantly reduces the overall weight while ensuring structural strength, facilitating transportation and installation; the 4.0-8.0 mm medium plate is mainly used for main support structures and connecting parts of ground power stations, and is particularly suitable for use in high wind pressure areas such as deserts, and its balanced mechanical properties and good cold bending formability facilitate the processing and manufacturing of complex structures; the 10.0-12.0 mm thick plate is specially designed for special high load scenarios such as rotating bases of large tracking supports and heavy support columns, providing long-term stable structural support for key load-bearing parts.

[0058] Further, the microstructure of the yield strength 345 MPa grade rare earth La weathering steel plate for photovoltaic support mainly consists of ferrite, pearlite and bainite. Compared with existing weathering steels, the difference in microstructure mainly lies in the content and distribution of bainite. The microstructure of traditional weathering steels is usually dominated by ferrite and pearlite, while this invention introduces a certain proportion of bainite structure by optimizing the composition and process. Specifically, the content of bainite is about 15%-25%, and it is uniformly distributed in the microstructure. The presence of this bainite not only improves the strength of the material, but also improves its toughness, while maintaining good corrosion resistance.

[0059] The distribution and proportion of these different phases are crucial to the mechanical properties and corrosion resistance of weathering steel. Figure 1 The microstructure of weathering steel sheet is shown. Ferrite is a brighter area with a body-centered cubic structure, providing toughness and ductility. Pearlite, composed of alternating layers of ferrite and cementite, appears as a darker layered structure, which has a negative impact on corrosion resistance. The lower the pearlite content, the denser the rust layer and the better the corrosion resistance. Bainite, with its needle-like or feather-like shape, is formed during rapid cooling and can significantly increase the strength and hardness of the steel. This combination of microstructures gives weathering steel sheet excellent overall performance, making it suitable for high-durability applications such as photovoltaic brackets.

[0060] Specifically, the distribution and proportion of this microstructure are controlled through composition design and rolling processes. For example, by adding appropriate amounts of alloying elements (such as Cu, Cr, Nb, etc.) and the rare earth element La, as well as controlling the cooling rate, the formation and distribution of ferrite, pearlite, and bainite can be effectively regulated. Furthermore, by controlling sulfur and oxygen content, the purity of the steel can be further improved, reducing the negative impact of non-metallic inclusions on performance.

[0061] Furthermore, the weathering steel plate was subjected to a 72-hour immersion accelerated corrosion test according to TB / T 2375-93 standard, and the corrosion rate was 1.8 to 2.2 g / m 2 h, meeting the TB / T 2375-93 weathering steel standard. This result demonstrates a corrosion resistance improvement of over 46% compared to ordinary carbon steel. In the low-corrosion environment of western China, weathering steel sheets can be used bare without galvanizing, reducing zinc consumption by 3.5 kg per ton of steel. This not only effectively reduces overall lifecycle costs but also minimizes environmental pollution during the galvanizing process. Compared to traditional hot-dip galvanized photovoltaic racks, these panels offer less environmental pollution and greater market competitiveness.

[0062] Specifically, the excellent corrosion resistance of the weathering steel plate of the present invention is mainly due to its unique alloy composition design, especially the addition of rare earth La. Experiments show that La releases La 3+ ions, effectively inhibiting corrosion reactions and significantly improving the corrosion resistance of the steel plate. In addition, the Cu element promotes the formation of a dense rust layer, the Cr element increases the corrosion potential and slows down the corrosion rate, and the Nb element optimizes the microstructure and indirectly improves the corrosion resistance. These elements work synergistically to form a dense protective rust layer on the surface of the steel plate, significantly enhancing the corrosion resistance. Therefore, in the C1 and C2 low-corrosion environments of the western region, the steel plate can effectively resist the erosion of corrosive media such as rain, moisture and salt spray, and extend its service life. Although the weathering steel plate of the present invention does not contain Ni, it exhibits excellent corrosion resistance comparable to that of traditional nickel-containing weathering steels in a variety of corrosion environments.

[0063] Furthermore, the 0°C impact energy KV2 of the weathering steel plate is ≥115J. This indicates that the steel plate can still maintain excellent impact resistance in low-temperature environments, effectively resisting external impacts, ensuring the structural stability and safety of photovoltaic brackets in cold climates, and is particularly suitable for use in western regions.

[0064] Furthermore, the weathering steel sheet exhibits excellent mechanical properties: yield strength ≥395 MPa, tensile strength ≥530 MPa, and elongation A ≥26%. By optimizing composition design and process control, the present invention achieves significant improvements in mechanical properties while simultaneously enhancing corrosion resistance, making it more suitable for high-durability applications such as photovoltaic brackets.

[0065] On the other hand, an embodiment of the present invention provides a method for preparing a weathering steel plate for a photovoltaic support with a yield strength of 345 MPa grade rare earth La, which is used to prepare the weathering steel plate described above, comprising the following steps:

[0066] S1: molten iron pretreatment;

[0067] S2: converter smelting;

[0068] S3: LF refining;

[0069] S4: continuous casting to obtain ingot;

[0070] S5. Hot rolling and subsequent treatment: The ingot is heated to 1190-1210°C and kept warm for 1.5-2.5 hours before hot rolling. It is then cooled under controlled conditions, coiled and leveled to obtain a yield strength 345MPa grade rare earth La weathering steel plate for photovoltaic supports.

[0071] The following is an introduction to the preparation method of the above-mentioned weathering steel plate in steps.

[0072] S1: Hot metal pretreatment

[0073] Before pre-treating the S1 molten iron, raw materials are prepared, including molten iron, lanthanum-iron alloy, electrolytic copper, metallic chromium, ferrosilicon, metallic manganese, ferroniobium, ferrophosphorus, and industrial pure iron, to construct a Cu-La-Cr ternary corrosion-resistant system. The molten iron is then pre-desulfurized using the KR method. The desulfurizer consists of CaO (90% by mass) and CaF2 (10% by mass). Compared to traditional desulfurizers, it exhibits better reaction activity and slag fluidity, and can more efficiently remove sulfur impurities. Ensure that the desulfurization slag clearing area is ≥95%, and that the sulfur content of the molten iron entering the furnace is ≤50ppm. This lays a solid foundation for subsequent low-sulfur steel production, meets the requirement for an extremely low sulfur content environment for the synergistic effect of rare earth La and other elements in steel, and avoids the adverse effects of sulfur on the corrosion resistance of rare earth elements and the purity of steel.

[0074] S2: Converter smelting

[0075] BOF smelting utilizes high-quality, low-sulfur scrap steel, strictly controlling its impurity content, such as sulfur and phosphorus, to ensure raw material purity. The final slag basicity is precisely controlled within the range of 3.5-3.7, with T.Fe ≤ 22%, ensuring an oxygen content of ≤ 600 ppm in the final molten steel. Compared to traditional BOF smelting, this precise control strategy effectively reduces inclusion formation in the molten steel, optimizes molten steel quality, and facilitates the subsequent uniform incorporation of rare earth elements and their synergistic formation with other alloying elements to form an ideal microstructure, ultimately enhancing the overall performance of the steel plate.

[0076] S3: LF Refining

[0077] During the LF refining process, white slag desulfurization is carried out, the slag basicity is controlled within the range of 5.5 to 6.5, the MI index (Mannesmann index) is 0.22 to 0.24, and the (FeO+MnO) content is guaranteed to be ≤0.8%, that is, the total content of FeO and MnO in the refining slag is less than 0.8%. The white slag treatment time is ≥30 minutes, which promotes the deep removal of impurities such as sulfur and oxygen in the molten steel and creates a high-quality environment for the precise alloying of rare earth La; the soft blowing time after calcium treatment is ≥10 minutes, and a lanthanum-iron alloy is added, the mass percentage of La in the lanthanum-iron alloy is 30%, and the oxygen content in the lanthanum-iron alloy is less than 0.006%, ensuring that the sulfur content of the molten steel after refining is ≤30ppm and the oxygen content is ≤30ppm, so as to reduce oxide inclusions in the steel.

[0078] S4: Continuous casting to obtain ingots

[0079] The molten steel is poured with double protection by using argon-sealed long water nozzle and magnesium oxide tundish covering agent, and the superheat of the molten steel is accurately controlled to 35℃~45℃.

[0080] S5: Hot rolling and subsequent processing

[0081] The ingot is heated to 1190-1210°C (e.g., 1190°C, 1195°C, 1200°C, 1205°C, 1210°C) and held for 1.5-2.5 hours. This heating regime is carefully designed based on the effect of rare earth La on the phase transformation of steel and the target structure of the steel plate of the present invention, ensuring that the ingot is fully austenitized and has a uniform structure, which is beneficial for subsequent rolling deformation. The starting temperature of hot rolling is strictly controlled at 1020-1080°C (e.g., 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C), and the finishing temperature is controlled at 860-875°C (e.g., 860°C, 862°C, 865°C, 870°C, 872°C, 875°C). Through precise rolling process control, precise control of the steel plate structure is achieved, allowing rare earth La and other alloying elements to form an ideal strengthening phase distribution during the rolling process.

[0082] Specifically, La and other rare earth elements can be solid-solved in the matrix of the steel, increasing the distortion of the matrix, thereby realizing solid-solution strengthening. Meanwhile, La can form fine spheroidized inclusions with other elements (such as S, O, Al, Ca, Ti, etc.), and these fine spheroidized inclusions can improve the impact toughness of the material and reduce the impact toughness low-temperature transition temperature. In addition, by controlling the heating and rolling temperature, La can also promote grain refinement, making the grain size uniform and fine, and further improving the comprehensive performance of the steel. This ideal strengthening phase distribution improves the strength and toughness of the steel, making it exhibit more excellent performance in practical applications.

[0083] Subsequently, controlled cooling, coiling and flattening are performed. The controlled cooling process adopts a staged water cooling mode. First, the hot-rolled billet is water-cooled to 580-620 DEG C (for example, 580 DEG C, 590 DEG C, 600 DEG C, 610 DEG C, 620 DEG C) at a relatively fast cooling rate (10-30 DEG C / s, for example, 12 DEG C / s, 15 DEG C / s, 18 DEG C / s, 20 DEG C / s, 25 DEG C / s, 28 DEG C / s) to promote grain refinement, and then air-cooled to room temperature. During the air-cooling process, rare earth La and other alloying elements (such as Ti, Nb, etc.) jointly affect the phase transition process of the steel, forming fine precipitates and uniform and dense microstructure. This synergistic effect not only optimizes the microstructure of the steel, but also significantly improves its corrosion resistance. Finally, a rare earth La weathering steel plate for photovoltaic support with a yield strength of 345 MPa is obtained.

[0084] Specifically, La combines with impurity elements such as oxygen and sulfur in the steel to form stable compounds, purifies the steel liquid, reduces non-metallic inclusions, and changes the morphology and distribution of inclusions, making them spheroidized and reducing the adverse effects on the performance of the steel. Second, La promotes the recrystallization and grain refinement of the steel during the rapid cooling stage, and by rapidly cooling to 580-620 DEG C, it helps to form uniform and fine grain size, further improving the strength and toughness of the steel.

[0085] The preparation process of the weathering steel of the present application relies on mature processes such as hot metal pretreatment, converter smelting, LF refining, continuous casting and hot continuous rolling, and the operation parameters of each link are clear, the production process is stable and efficient. Since common mature technologies are used, no additional professional training is required, which is suitable for large-scale industrial production and further improves the market competitiveness.

[0086] In summary, the weathering steel plate of the present invention reduces production costs by adding rare earth element La to replace expensive nickel (Ni) and adjusting the content of copper (Cu) and chromium (Cr), so that the alloy cost is reduced by 22% compared with traditional weathering steel and 15% lower than the full life cycle cost of hot-dip galvanized steel. In the 72-hour weekly immersion corrosion test under the TB / T 2375-93 standard, the corrosion rate of the Ni-free weathering steel of the present invention is 1.8~2.2g / m2·h, which meets the corrosion performance requirements of the weathering steel standard and can be used without galvanizing in the low-corrosion environment in the west, reducing environmental pollution and costs. The Cu-La-Cr ternary corrosion-resistant system constructed by the present invention improves the density and corrosion resistance of the rust layer. Weathering steel has excellent mechanical properties, with a yield strength exceeding 395MPa, a tensile strength exceeding 530MPa, an elongation of more than 26%, and a low-temperature impact energy KV2 of more than 115J, which ensures the safety and stability of photovoltaic brackets under different climatic conditions and enhances market competitiveness.

[0087] The present invention is described in more detail below through specific examples. The examples are merely descriptions of the best mode of carrying out the present invention and do not limit the scope of the present invention in any way.

[0088] Examples 1 to 4

[0089] Embodiments 1 to 4 of the present invention provide a weathering steel plate for a photovoltaic support with a yield strength of 345 MPa and a preparation method thereof.

[0090] The components of the rare earth La weathering steel plates of Examples 1 to 4 include, by mass percentage, C: 0.12% to 0.15%, Si: 0.20% to 0.40%, Mn: 0.30% to 0.50%, P: ≤0.0180%, S: ≤0.0028%, O: ≤0.0032%, La: 0.0052% to 0.0350%, Cu: 0.13% to 0.25%, Cr: 0.48% to 0.90%, Nb: 0.022% to 0.050%, and the balance is Fe and unavoidable impurities.

[0091] The preparation method of the rare earth La weathering steel plate of Examples 1 to 4 includes:

[0092] S1: Hot metal pretreatment

[0093] The KR method is used to pre-desulfurize the molten iron. The desulfurizer is composed of CaO (90% by mass) and CaF2 (10% by mass). It is ensured that the desulfurization slag cleaning area is ≥95% and the sulfur content of the molten iron entering the furnace is ≤50ppm.

[0094] S2: Converter smelting

[0095] Low-sulfur scrap steel is used in converter smelting, and the final slag basicity is controlled within the range of 3.5-3.7, T.Fe≤22%, ensuring that the oxygen content of the final molten steel is ≤600ppm.

[0096] S3: LF Refining

[0097] During the LF refining process, white slag desulfurization is carried out, the slag basicity is controlled within the range of 5.5 to 6.5, the MI index (Mannesmann index) is 0.22 to 0.24, and the (FeO+MnO) content is guaranteed to be ≤0.8%, that is, the total content of FeO and MnO in the refining slag is less than 0.8%, and the white slag treatment time is ≥30 minutes; the soft blowing time after calcium treatment is ≥10 minutes, and lanthanum iron alloy is added to ensure that the sulfur content of the molten steel after refining is ≤30ppm and the oxygen content is ≤30ppm, so as to reduce oxide inclusions in the steel.

[0098] S4: Continuous casting to obtain ingots

[0099] The molten steel is protected by an argon-sealed long water nozzle and a magnesium oxide tundish covering agent, and the superheat of the molten steel is precisely controlled to 35℃~45℃.

[0100] S5: Hot rolling and subsequent processing

[0101] The ingot is heated to 1190-1210°C and kept warm for 1.5-2.5 hours before hot rolling. The starting rolling temperature of hot rolling is controlled at 1020-1080°C, and the final rolling temperature is controlled at 860-875°C. Subsequently, controlled cooling, coiling and leveling are carried out. The controlled cooling process adopts a graded water cooling mode. The hot-rolled steel billet is first water-cooled to 580-620°C at a faster cooling rate (10-30°C / s) to promote grain refinement, and then air-cooled to room temperature. Finally, a rare earth La weathering steel plate for photovoltaic brackets with a yield strength of 345MPa is obtained.

[0102] Table 1 shows the process parameters of the embodiments and comparative examples.

[0103] Table 1

[0104]

[0105] Comparative Examples 1-4: This invention provides several comparative examples to demonstrate the effects of different elements on the corrosion resistance of weathering steel. Comparative Example 1 uses ordinary carbon steel as a baseline for corrosion resistance comparison; Comparative Example 2 uses weathering steel without the rare earth element La to illustrate the significant improvement in corrosion resistance of the material; Comparative Example 3 uses weathering steel with the rare earth element Ce added but without La to demonstrate the advantages of adding La alone; and Comparative Example 4 uses weathering steel with only Cr added but without Cu to demonstrate the importance of the synergistic effect of Cu and Cr on corrosion resistance.

[0106] The chemical compositions of the steel plates of the examples and comparative examples are shown in Table 2.

[0107] Table 2 Chemical composition, wt%

[0108]

[0109] The mechanical properties of the examples and comparative examples are shown in Table 3.

[0110] Table 3 Mechanical properties

[0111] serial number [R m / MPa]]> <![CDATA[R p0.2 / MPa]]> A / ％ <![CDATA[KV2(J,0℃)]]> Example 1 531 396 30 128 Example 2 531 412 31 128 Example 3 541 422 28 122 Example 4 547 423 26 119 Comparative Example 1 490 375 31 102 Comparative Example 2 525 411 31 121 Comparative Example 3 520 415 30 124 Comparative Example 4 513 407 30 127

[0112] To demonstrate the corrosion resistance of the steel plates of the present invention, the corrosion resistance of the steels of the examples and comparative examples was measured using 72-hour cyclic immersion accelerated corrosion test data (test standard TB / T2375-93). This experiment was used to evaluate the corrosion resistance of the steel plates of the present invention. The results of the corrosion test are shown in Table 4.

[0113] Table 4 Corrosion rate data of the weekly immersion accelerated corrosion test

[0114]

[0115]

[0116] From Table 2 and Table 4, it can be seen that: Comparative Example 2 adds Cu and Cr to the corrosion-resistant elements compared to Comparative Example 1, and its corrosion resistance is only improved by 43.6% compared to carbon steel, which does not reach the minimum standard of weathering steel (>45%). On the other hand, Examples 1-2 add rare earth La on the basis of Comparative Example 2, and the content of other components remains basically unchanged, and the corrosion resistance reaches the standard of weathering steel, which shows that the addition of La plays an important role in improving corrosion resistance. Comparative Example 3 adds Ce and Example 1 adds La, and the content of other elements remains basically unchanged. The corrosion resistance of Example 1 is significantly higher than that of Comparative Example 3, which shows that La improves the weather resistance of steel materials better than Ce. Comparative Example 4 does not add the Cu element, and the content of other elements is basically the same as that of Example 1. The weather resistance of Comparative Example 4 is greatly reduced, indicating that the Cu element has a significant effect on the weather resistance of steel materials.

[0117] Comparative Example 2 (without La) is compared with Examples 1 to 4. The 72-hour immersion corrosion rates of Examples 1 to 4 are 2.195, 2.025, 1.893, and 1.811 g / m2, respectively. 2 h, compared with 2.327 g / m2 in Comparative Example 2 2·h, the corrosion resistance increased by 5.6%, 12.9%, 18.6% and 22.1% respectively, which proves that La significantly improves the corrosion resistance; Comparative Example 3 (using Ce to replace La) is compared with Example 1. The 72-hour weekly immersion corrosion rate of Example 1 is 2.195g / m2·h, compared with 2.277g / m2·h of Comparative Example 3, the corrosion resistance is improved by 3.6%, indicating that the synergistic effect of La is better than that of Ce; Comparative Example 4 (no Cu) is compared with Example 1. The 72-hour weekly immersion corrosion rate of Example 1 is 2.195g / m2·h, compared with 2.85g / m 2 h, the corrosion resistance is improved by 23.0%, indicating that Cu is an essential component of the Cu-La synergistic effect. The combination of the three indirectly proves the uniqueness of the Cu-La-Cr ternary system.

[0118] Furthermore, as the rare earth La content in Examples 1-4 gradually increased within the range of 0.025% to 0.035%, the corrosion resistance of the test steels also gradually improved, demonstrating a positive correlation between La content and corrosion resistance. In Examples 3-4, based on Examples 1-2, the rare earth La, Cu, and Cr contents were further increased, resulting in corrosion resistance improvements of 54.1% and 56.1%, respectively, compared to carbon steel, and a service life more than doubled that of carbon steel.

[0119] Overall, the 72-hour immersion corrosion rate of Examples 1 to 4 is 1.8 to 2.2 g / m 2 h. The corrosion resistance of weathering steel plate is improved by more than 46% (e.g., 46.8% to 56.1%) compared with ordinary carbon steel, showing excellent corrosion resistance, which proves the effectiveness of the present invention in improving the corrosion resistance of weathering steel.

[0120] As shown in Table 3, the weathering steel of the present invention has excellent mechanical properties, including a yield strength of 395 MPa or greater (e.g., 396 MPa to 423 MPa), a tensile strength of 530 MPa or greater (e.g., 531 MPa to 547 MPa), an elongation (A) of 26% or greater (e.g., 26% to 31%), and a 0°C impact energy (KV2) of 115 J or greater (e.g., 119 J to 128 J). These performance indicators fully meet the requirements for photovoltaic support applications, ensuring structural stability and reliability.

[0121] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A weathering steel plate with a yield strength of 345MPa grade rare earth La for photovoltaic support, characterized in that: The components of the weathering steel plate for the rare earth La photovoltaic bracket with a yield strength of 345MPa include, in mass percentage, C: 0.12% to 0.15%, Si: 0.20% to 0.40%, Mn: 0.30% to 0.50%, P: ≤0.018%, S: ≤0.0028%, O: ≤0.0032%, La: 0.0052% to 0.0350%, Cu: 0.13% to 0.25%, Cr: 0.48% to 0.90%, Nb: 0.022% to 0.050%, and the remainder is Fe and unavoidable impurities.

2. The yield strength 345MPa grade rare earth La weathering steel plate for photovoltaic support according to claim 1, characterized in that: The components of the weathering steel plate for the yield strength 345MPa grade rare earth La photovoltaic bracket include, in mass percentage, C: 0.12%~0.15%, Si: 0.20%~0.40%, Mn: 0.30%~0.50%, P: ≤0.010%, S: ≤0.0028%, O: ≤0.0032%, La: 0.0052%~0.0250%, Cu: 0.13%~0.25%, Cr: 0.60%~0.90%, Nb: 0.030%~0.040%, and the balance is Fe and unavoidable impurities.

3. The weathering steel plate for photovoltaic support with a yield strength of 345 MPa grade rare earth La according to claim 1, characterized in that: The thickness of the weathering steel plate with a yield strength of 345 MPa grade rare earth La for photovoltaic brackets is 1.5 to 12 mm.

4. The yield strength 345MPa grade rare earth La weathering steel plate for photovoltaic support according to claim 1, characterized in that: The microstructure of the 345MPa yield strength rare earth La weathering steel plate for photovoltaic supports is ferrite, pearlite and bainite.

5. The weathering steel plate for photovoltaic support with a yield strength of 345 MPa grade rare earth La according to claim 1, characterized in that: The yield strength 345MPa grade rare earth La weathering steel plate for photovoltaic bracket was subjected to 72 hours of immersion accelerated corrosion test according to TB / T 2375-93 standard, and the corrosion rate was 1.8-2.2g / m 2 ·h.

6. The yield strength 345MPa grade rare earth La weathering steel plate for photovoltaic support according to claim 1, characterized in that: The yield strength of the 345MPa grade rare earth La weathering steel plate for photovoltaic supports is ≥395MPa, the tensile strength reaches ≥530MPa, and the elongation A is ≥26%.

7. The yield strength 345MPa grade rare earth La weathering steel plate for photovoltaic support according to claim 1, characterized in that: The 0°C impact energy KV2 of the 345MPa yield strength rare earth La weathering steel plate for photovoltaic supports is ≥115J.

8. A method for preparing a weathering steel plate with a yield strength of 345 MPa grade rare earth La for photovoltaic support, characterized in that: The preparation method is used to prepare the 345 MPa yield strength rare earth La weathering steel plate for photovoltaic supports according to any one of claims 1 to 7, comprising the following steps: S1: molten iron pretreatment; S2: converter smelting; S3: LF refining; S4: continuous casting to obtain ingot; S5. The ingot is heated to 1190-1210° C. and kept warm for 1.5-2.5 hours, and then hot-rolled. The ingot is then controlled cooled, coiled, and flattened to obtain a weathering steel plate with a yield strength of 345 MPa grade rare earth La for photovoltaic supports.

9. The method for preparing a weathering steel plate with a yield strength of 345 MPa grade rare earth La for photovoltaic support according to claim 8, characterized in that: In S1, the KR method is used for pre-desulfurization treatment, the desulfurizer is a CaO+CaF2 mixture, and the sulfur content of the molten iron is controlled at ≤50ppm; in S3, white slag desulfurization is carried out, the slag basicity is 5.5-6.5, the sulfur content of the molten steel after refining is ≤30ppm, the oxygen content is ≤30ppm, and lanthanum iron alloy is added to achieve precise micro-alloying of La.

10. The method for preparing a weathering steel plate with a yield strength of 345 MPa grade rare earth La for photovoltaic support according to claim 9, characterized in that: In S5, the starting rolling temperature of the hot rolling is 1020-1080°C, and the finishing rolling temperature is 860-875°C; the controlled cooling includes: first water cooling the hot-rolled steel billet to 580-620°C at a cooling rate of 10-30°C / s, and then air cooling to room temperature.

Images