Hot-rolled weather-resistant steel plate for 355MPa-grade photovoltaic bracket and preparation method of hot-rolled weather-resistant steel plate

Abstract

The invention discloses a hot-rolled weather-resistant steel plate for a 355MPa-level photovoltaic support and a preparation method of the hot-rolled weather-resistant steel plate, and belongs to the technical field of steelmaking. In order to improve the corrosion resistance of the steel plate, the invention provides a hot-rolled weather-resistant steel plate for a 355MPa-grade photovoltaic bracket and a preparation method, and the steel plate comprises the following components: 0.06 to 0.09 percent of C, 0.35 to 0.45 percent of Si, 0.45 to 0.55 percent of Mn, 0.070 to 0.080 percent of P, less than or equal to 0.008 percent of S, 1.10 to 1.20 percent of Cr, 0.25 to 0.35 percent of Cu and 0.020 to 0.060 percent of Als. The method comprises the following steps: smelting the components into a plate blank, and then sequentially heating, roughly rolling, finely rolling, laminar cooling and coiling to obtain the steel plate. The components of the steel plate are optimized, meanwhile, heating, rolling and other processes are improved, the obtained steel plate has excellent mechanical properties, the corrosion resistance is remarkably improved, and the production cost is remarkably reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking, and specifically relates to a 355MPa-grade hot-rolled weathering steel plate for a photovoltaic support and a preparation method thereof. Background Art

[0002] In order to achieve the "dual carbon" goal, non-fossil energy such as photovoltaics will accelerate the transition from supplementary energy to alternative energy. According to the "China Photovoltaic Industry Development Roadmap (2023-2024)" released by the China Photovoltaic Industry Association, the country's new photovoltaic grid-connected installed capacity will be 216.88GW in 2023, and the cumulative photovoltaic grid-connected installed capacity will exceed 600GW. Both the new and cumulative installed capacity are the first in the world, so the photovoltaic industry has broad development space for steel.

[0003] Photovoltaic brackets are important supporting and protective structures for photovoltaic power generation devices. The choice of bracket materials directly affects the operational safety, breakage rate, construction investment and later maintenance costs of photovoltaic modules. Photovoltaic power stations are generally built in areas with harsh environments such as coastal beaches, deserts, Gobi and water surfaces, and may be subject to extreme weather conditions such as strong winds, hail, and heavy snow. According to the "Photovoltaic Bracket Structure Design Code" (NB / T 10115-2018), the design service life of photovoltaic brackets in photovoltaic power stations should be no less than 25 years, so very high requirements are placed on the bearing capacity and corrosion resistance of photovoltaic brackets. Photovoltaic brackets are generally made of aluminum alloys, stainless steel, hot-dip galvanized steel parts, etc., which generally have problems such as high cost, difficulty in recycling, and serious environmental pollution caused by the galvanizing process.

[0004] In order to meet the new requirements of the photovoltaic industry for low-cost, green, and highly corrosion-resistant photovoltaic brackets, and to achieve reliable service of photovoltaic brackets in harsh environments, highly corrosion-resistant weathering steel has entered the field of vision of photovoltaic users. After long-term exposure to the atmosphere, a layer of well-protected oxidation products will be generated on the surface of weathering steel to isolate the steel matrix from external corrosive substances, thereby significantly improving the corrosion resistance of weathering steel. Therefore, the application of weathering steel in photovoltaic brackets can be exposed or reduced in coating according to the actual service environment, thereby reducing the coating process, construction cycle, maintenance process and environmental pollution, and extending the service life of photovoltaic brackets.

[0005] CN114438411A discloses a weathering steel for photovoltaic brackets and a production method thereof, wherein precious metal elements Ni (0.05-0.30%) and Nb (0.01-0.05%) are added to the steel, the Mn element content is relatively high (0.3-1.20%), and the Ti element (0.010-0.030%) is added; according to the embodiments, the atmospheric corrosion resistance index of the product is 6.37-6.6, and the corrosion resistance is difficult to meet the requirements for exposed use in photovoltaic brackets.

[0006] CN115747644A discloses a rare earth weathering steel for photovoltaic brackets and a production method thereof. The steel is added with precious metal elements Ni (0.05-0.15%), a high content of Mn (0.8-1.0%), and Ti (0.020-0.030%) and La (15-25 ppm). According to the chemical composition of the product, its corrosion resistance is difficult to meet the requirements for exposed use in photovoltaic brackets. Summary of the invention

[0007] The purpose of the present invention is to improve the corrosion resistance of a steel plate for a photovoltaic support, ensure its mechanical properties, and reduce production costs.

[0008] To achieve the above object, the present invention first provides a method for preparing a 355MPa hot-rolled weathering steel plate for a photovoltaic support, wherein the 355MPa hot-rolled weathering steel plate for a photovoltaic support comprises the following components by weight percentage: C 0.06-0.09%, Si 0.35-0.45%, Mn 0.45-0.55%, P 0.070-0.080%, S≤0.008%, Cr 1.10-1.20%, Cu 0.25-0.35%, Als 0.020-0.060%, and the balance is Fe and unavoidable impurities;

[0009] The preparation method comprises the following steps: smelting the required components into slabs, and then sequentially heating, rough rolling, finish rolling, laminar cooling and coiling the slabs to obtain the slabs.

[0010] Among them, in the preparation method of the above-mentioned 355MPa-grade hot-rolled weathering steel plate for photovoltaic support, the thickness of the 355MPa-grade hot-rolled weathering steel plate for photovoltaic support is 1.5 to 6.0 mm.

[0011] Among them, in the preparation method of the above-mentioned 355MPa grade hot-rolled weathering steel plate for photovoltaic support, in the heating step, the slab is hot-delivered and hot-loaded, the heating temperature is 1220-1260°C, and the heating time is 130-230min.

[0012] Among them, in the preparation method of the above-mentioned 355MPa-grade hot-rolled weathering steel plate for photovoltaic brackets, in the rough rolling step, after 6 rough rolling passes, the deformation amount of each pass is ≥18%; when the thickness of the finished hot-rolled weathering steel plate is 1.5mm≤thickness<2.5mm, the thickness of the intermediate billet is controlled to be 30-34mm; when the thickness of the finished hot-rolled weathering steel plate is 2.5mm≤thickness<4.0mm, the thickness of the intermediate billet is controlled to be 32-36mm; when the thickness of the finished hot-rolled weathering steel plate is 4.0-6.0mm, the thickness of the intermediate billet is controlled to be 40-44mm.

[0013] Among them, in the preparation method of the above-mentioned 355MPa grade hot-rolled weathering steel plate for photovoltaic bracket, in the finishing rolling step, after 7 finishing rolling passes, the reduction rates of the last three stands are ≥15%, ≥13% and ≥10% respectively, and the final rolling temperature is 860-900℃.

[0014] Among them, in the preparation method of the above-mentioned 355MPa-grade hot-rolled weathering steel plate for photovoltaic support, a front-stage cooling mode is adopted in the laminar cooling step, and the cooling rate is ≥40°C / s.

[0015] Among them, in the preparation method of the above-mentioned 355MPa grade hot-rolled weathering steel plate for photovoltaic support, in the coiling step, the coiling temperature is 580-620°C.

[0016] The present invention also provides a 355MPa-grade hot-rolled weathering steel plate for a photovoltaic support, which is prepared by the above-mentioned preparation method.

[0017] Among them, the above-mentioned 355MPa-grade hot-rolled weathering steel plate for photovoltaic bracket has a yield strength ≥355MPa, a tensile strength ≥490MPa, an elongation after fracture ≥25%, and a 180° bending test D=a.

[0018] Among them, the above-mentioned 355MPa grade hot-rolled weathering steel plate for photovoltaic bracket has an atmospheric corrosion resistance index I≥7.5, a relative Q355B corrosion rate≤35%, and a double-sided uniform corrosion thinning amount of no more than 0.2mm during a 25-year service life under a C1-C3 environment.

[0019] In the present invention, all steps not specifically described are performed using conventional operations in the art.

[0020] Beneficial effects of the present invention:

[0021] The present invention adds a certain amount of Si, P, Cr, Cu and other elements to make the atmospheric corrosion resistance index I≥7.5, thereby significantly improving the atmospheric corrosion resistance of the product. Compared with traditional weathering steel, the alloy cost is effectively reduced because the Ni element is not added. By giving full play to the solid solution strengthening effect of Si, P and other elements, no Nb, Ti and other elements are added, and the Mn element content is reduced, so that the alloy cost is further reduced. By setting a reasonable heating temperature and heating time, the performance is guaranteed and the generation of "copper brittleness" defects is avoided. By a reasonable production process design, the stable production of thin-gauge products and the control of organizational performance are guaranteed.

[0022] The hot-rolled weathering steel plate for photovoltaic brackets prepared by the composition and preparation method of the present invention has a yield strength of ≥355MPa, a tensile strength of ≥490MPa, an elongation after fracture of ≥25%, a 180° bending test D=a, a relative Q355B corrosion rate of ≤35%, and a double-sided uniform corrosion thinning amount of no more than 0.2mm within a bare 25-year service life under the C1-C3 environment specified in "Atmospheric Corrosion of Metals and Alloys Part 1: Classification, Determination and Evaluation" (GB / T 19292.1-2018). Application to photovoltaic brackets can effectively reduce transportation costs, construction cycles, and painting and maintenance costs, thereby achieving green applications. DETAILED DESCRIPTION

[0023] Specifically, a method for preparing a 355MPa-grade hot-rolled weathering steel plate for a photovoltaic support, wherein the 355MPa-grade hot-rolled weathering steel plate for a photovoltaic support comprises the following components by weight percentage: C 0.06-0.09%, Si 0.35-0.45%, Mn 0.45-0.55%, P 0.070-0.080%, S≤0.008%, Cr 1.10-1.20%, Cu 0.25-0.35%, Als 0.020-0.060%, and the balance is Fe and unavoidable impurities;

[0024] The preparation method comprises the following steps: smelting the required components into slabs, and then sequentially heating, rough rolling, finish rolling, laminar cooling and coiling the slabs to obtain the slabs.

[0025] Functions and mechanisms of each element and main process in the present invention:

[0026] Carbon: Carbon is an effective strengthening element in steel. It can be dissolved into the matrix to play a role of solid solution strengthening, and can combine with titanium to form carbide precipitation particles, which play a role of fine grain strengthening and precipitation strengthening. Therefore, increasing the carbon content is beneficial to improving strength. However, too high a carbon content is likely to form a segregation zone in the center of the steel plate, and when the cooling rate is high, a martensitic structure is likely to form at the segregation zone, resulting in reduced bending performance, impact performance, and forming performance. Therefore, the value range of C in the present invention is set to 0.06-0.09%.

[0027] Silicon: Silicon can be dissolved in ferrite and austenite to improve the hardness and strength of steel, which is beneficial to refine the rust layer structure and reduce the overall corrosion rate of steel. However, too high a content will reduce the plasticity and toughness of the steel and make it difficult to remove scale during rolling. Therefore, the value range of Si in the present invention is set to 0.35-0.45%.

[0028] Manganese: Manganese has a strong solid solution strengthening effect, can significantly reduce the phase transition temperature of steel, refine the microstructure of steel, and is an important strengthening element. However, when the manganese content is too high, the continuous casting process is prone to cracks in the ingot, and may cause component segregation in the core of the steel plate, resulting in reduced bending performance, impact performance, and forming performance, while increasing production costs. Therefore, the value range of Mn in the present invention is set to 0.45-0.55%.

[0029] Phosphorus: Although phosphorus has a strong solid solution strengthening effect and can effectively improve the atmospheric corrosion resistance of steel with low cost, excessive phosphorus content will significantly reduce the plasticity and low temperature toughness of steel. Therefore, the value range of P in the present invention is set to 0.070-0.080%.

[0030] Sulfur: Sulfur will have an adverse effect on the structure and properties of steel plates. Too high a sulfur content will increase the hot brittleness tendency of steel. At the same time, sulfur will form sulfide inclusions that deteriorate the properties of steel. Therefore, the value range of S in the present invention is set to S≤0.008%.

[0031] Chromium: Chromium has a significant effect on improving the passivation ability of steel, and can promote the formation of a dense passivation film or protective rust layer on the steel surface. Its enrichment in the rust layer can effectively improve the selective permeability of the rust layer to corrosive media; however, too high a chromium content will increase production costs, and at a high cooling rate, it is easy to cause martensite structure to be produced, which reduces the plasticity and toughness of the steel. Therefore, the value range of Cr in the present invention is set to 1.10-1.20%.

[0032] Copper: copper added to steel is conducive to forming a dense, well-adhesive amorphous oxide (hydrocarbon oxide) protective layer on the surface of the steel, which has a significant corrosion resistance effect; in addition, copper and sulfur form insoluble sulfides, thereby offsetting the harmful effects of S on the corrosion resistance of steel; however, when the copper content is too high, due to the low melting point of copper, which is lower than the heating temperature of the steel billet, the precipitated copper is in liquid and aggregates at the austenite grain boundary. When the precipitated copper content reaches a certain level, it is easy to produce cracks during heating or hot rolling, that is, "copper brittleness" defects; in addition, according to the calculation formula of the atmospheric corrosion resistance index I, too little or too much copper content will reduce the calculated value of I. Therefore, the value range of Cu in the present invention is set to 0.25-0.35%.

[0033] Aluminum: Aluminum is added to steel to deoxidize and improve the quality of steel. However, if the aluminum content is too high, its nitrogen oxides are easily precipitated at the austenite grain boundaries, causing cracks in the casting. Therefore, the value range of Als in the present invention is set to 0.020-0.060%.

[0034] In the preparation method of 355MPa grade hot-rolled weathering steel plate for photovoltaic support disclosed in the present invention, the composition of the 355MPa grade hot-rolled weathering steel plate for photovoltaic support described in the above content is smelted into a slab, and then the slab is heated, rough-rolled, finish-rolled, laminar-cooled and coiled in sequence to obtain the 355MPa grade hot-rolled weathering steel plate for photovoltaic support.

[0035] Further specifically, in the heating step, the slab is heated in a regenerative heating furnace. The purpose of heating the slab is to homogenize the as-cast structure and component segregation, and to dissolve the alloy elements at the same time; however, too high a heating temperature and too long a heating time will lead to coarse austenite grains, as well as problems such as burning, overheating, and overburning; at the same time, compared with traditional weathering steel, in order to reduce the alloy cost, a certain amount of Cu is added to the hot-rolled weathering steel plate for 355MPa-grade photovoltaic brackets of the present invention without adding Ni, and a Ni-containing copper-rich phase cannot be formed to reduce the chance of liquid copper-rich phase formation. Therefore, too long a heating time will lead to "copper brittleness" defects. Therefore, in the present invention, the casting is required to be hot-sent and hot-loaded in the heating step, and the heating temperature is set to 1220-1260°C and the heating time is 130-230min.

[0036] In the present invention, the thickness of the finished 355MPa-grade hot-rolled weathering steel plate for photovoltaic support is 1.5 to 6.0 mm.

[0037] To be more specific, in the rough rolling step, the rough rolling needs to achieve sufficient deformation to ensure austenite recrystallization, refine austenite grains, and prevent the appearance of mixed crystal structure. If the thickness of the intermediate billet is too small, the deformation of the finishing rolling may be insufficient; if the thickness of the intermediate billet is too large, the deformation of the rough rolling may be insufficient; in addition, when the thickness of the finished product is small, the temperature drop of the strip during the finishing rolling process is relatively fast, and the thickness of the intermediate billet can be appropriately reduced to avoid excessive finishing load while ensuring sufficient finishing deformation. Therefore, the present invention sets the rough rolling step to undergo 6 rough rolling passes, with a deformation of ≥18% per pass; when the thickness of the finished product is 1.5~<2.5mm, the thickness of the intermediate billet is 30~34mm; when the thickness of the finished product is 2.5~<4.0mm, the thickness of the intermediate billet is 32~36mm; when the thickness of the finished product is 4.0~6.0mm, the thickness of the intermediate billet is 40~44mm.

[0038] To be more specific, in the finishing step, the three stands after finishing rolling are basically rolled in the austenite non-recrystallization zone. By adopting a large deformation rate, the austenite grains that have been rolled in the recrystallization zone and refined to a certain extent can be flattened and elongated, increasing the grain boundary area of ​​austenite per unit volume. At the same time, a large number of deformation bands and high-density dislocations will be generated in the grains, thereby increasing the ferrite nucleation rate and obtaining a fine structure after phase transformation; if the final rolling temperature is too low, there is a risk of rolling in the two-phase zone in the last few stands after finishing rolling, especially due to the difference in temperature in the width direction of the strip, the edge temperature is often lower, and as the thickness of the strip decreases, the temperature of the finishing rolling process drops faster. When the last few stands are rolled in the last few stands, the edge temperature of the strip is easily reduced to the austenite-ferrite two-phase zone, resulting in a mixed crystal structure that makes the comprehensive performance of the product worse; if the final rolling temperature is too high, the deformation of the non-recrystallization zone rolled in the last few stands after finishing rolling is insufficient, which is not conducive to the final structure refinement. Therefore, the present invention sets the finishing rolling step to be carried out through 7 passes, the reduction rates of the last three stands are ≥15%, ≥13% and ≥10% respectively, and the final rolling temperature is 860-900°C.

[0039] Specifically speaking, in the laminar cooling step, the front cooling mode is adopted, and the cooling rate is controlled to be ≥40℃ / s, which can achieve a large degree of supercooling to refine the final structure, and the use of a large cooling rate can have a certain improvement effect on the core band structure. After the strip steel leaves the finishing mill, it enters the laminar cooling section. In the laminar cooling section, the strip steel is cooled from the finishing rolling temperature to the coiling temperature by water spray cooling and air cooling, and then coiled. Water spray cooling in the front section of the laminar cooling section is the front cooling mode.

[0040] In the coiling step, if the coiling temperature is too low, the cooling rate will be too high during the cooling process, resulting in the formation of martensite structure, which will reduce plasticity and toughness; if the coiling temperature is too high, the grains and second phase particles will be coarse, resulting in reduced strength, plasticity and toughness. Therefore, the coiling temperature is set to 580-620°C in the present invention.

[0041] From the above, it can be seen that the present invention optimizes the composition of the steel plate, adds a certain amount of Si, P, Cr, Cu and other elements, does not add precious elements such as Ni, Nb, Ti, and improves the process at the same time to match the process and the composition, thereby obtaining a 355MPa grade hot-rolled weathering steel plate for photovoltaic brackets. The steel plate has excellent mechanical properties and corrosion resistance that is significantly better than existing steel plates, and greatly reduces production costs.

[0042] The 355MPa-grade hot-rolled weathering steel plate for photovoltaic brackets provided by the present invention has a yield strength of ≥355MPa, a tensile strength of ≥490MPa, an elongation after fracture of ≥25%, and a 180° bending test D=a.

[0043] The 355MPa-grade hot-rolled weathering steel plate for photovoltaic brackets provided by the present invention has an atmospheric corrosion resistance index I≥7.5, a relative Q355B corrosion rate≤35%, and a double-sided uniform corrosion thinning amount of no more than 0.2mm during a 25-year service life in a bare use under a C1-C3 environment.

[0044] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is not limited to the scope of the examples.

[0045] In the embodiment, the atmospheric corrosion resistance index of the hot-rolled weathering steel plate for photovoltaic bracket is I=26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.10(%Ni)(%P)-33.39(%Cu) 2 .

[0046] In the embodiment, the yield strength, tensile strength and elongation of the hot-rolled weathering steel plate for the photovoltaic support are tested according to "Tensile Test of Metallic Materials Part 1: Room Temperature Test Method" (GB / T 228.1); the bending performance is tested according to the "Metallic Material Bending Test Method" (GB / T 232); the corrosion resistance is tested according to Appendix B of "Special Metal Materials for Locomotives and Rolling Stocks - Atmospheric Corrosion Resistant Steel" (TB / T 1979-2023).

[0047] Example 1

[0048] The chemical composition of the 355MPa grade hot-rolled weathering steel plate for photovoltaic support in this embodiment is shown in Table 1, and the remainder is Fe and unavoidable impurities.

[0049] The 355MPa grade hot-rolled weathering steel plate for photovoltaic support of this embodiment is smelted into slabs by conventional methods according to its composition, and the smelted slabs are further processed, and heating, rough rolling, finishing rolling, laminar cooling and coiling are performed in sequence. The specific processing technology is as follows: the ingot is hot-transferred and hot-loaded, the heating temperature is 1255°C, and the heating time is 200min; after 6 rough rolling passes, the deformation amount of each pass is 18%, 26%, 30%, 29%, 31%, and 23% respectively, and the thickness of the intermediate slab is 32mm; after 7 finishing rolling passes, the reduction rates of the last three stands are 15%, 13%, and 10% respectively, and the final rolling temperature is 880-900°C; the front-stage cooling mode is adopted, the cooling rate is 50°C / s, and the coiling temperature is 590-620°C.

[0050] The specific properties of the 355MPa grade hot-rolled weathering steel plate for photovoltaic support obtained in this embodiment are shown in Table 2.

[0051] Example 2

[0052] The chemical composition of the 355MPa grade hot-rolled weathering steel plate for photovoltaic support in this embodiment is shown in Table 1, and the remainder is Fe and unavoidable impurities.

[0053] The 355MPa grade hot-rolled weathering steel plate for photovoltaic support of this embodiment is smelted into slabs by conventional methods according to its composition, and the smelted slabs are further processed, and heating, rough rolling, finishing rolling, laminar cooling and coiling are performed in sequence. The specific processing technology is as follows: the ingot is hot-delivered and hot-loaded, the heating temperature is 1245°C, and the heating time is 180min; after 6 rough rolling passes, the deformation of each pass is 18%, 26%, 28%, 28%, 27%, and 25%, respectively, and the thickness of the intermediate slab is 34mm; after 7 finishing rolling passes, the reduction rates of the last three stands are 16%, 14%, and 11%, respectively, and the final rolling temperature is 870-885°C; the front-stage cooling mode is adopted, the cooling rate is 50°C / s, and the coiling temperature is 590-605°C.

[0054] The specific properties of the 355MPa grade hot-rolled weathering steel plate for photovoltaic support obtained in this embodiment are shown in Table 2.

[0055] Example 3

[0056] The chemical composition of the 355MPa grade hot-rolled weathering steel plate for photovoltaic support in this embodiment is shown in Table 1, and the remainder is Fe and unavoidable impurities.

[0057] The 355MPa grade hot-rolled weathering steel plate for photovoltaic support of this embodiment is smelted into slabs by conventional methods according to its composition, and the smelted slabs are further processed, and heating, rough rolling, finishing rolling, laminar cooling and coiling are performed in sequence. The specific processing technology is as follows: the ingot is hot-delivered and hot-loaded, the heating temperature is 1230°C, and the heating time is 170min; after 6 rough rolling passes, the deformation of each pass is 18%, 23%, 25%, 24%, 24%, and 23%, respectively, and the thickness of the intermediate slab is 42mm; after 7 finishing rolling passes, the reduction rates of the last three stands are 15%, 14%, and 11%, respectively, and the final rolling temperature is 865-890°C; the front-stage cooling mode is adopted, the cooling rate is 45°C / s, and the coiling temperature is 595-615°C.

[0058] The specific properties of the 355MPa grade hot-rolled weathering steel plate for photovoltaic support obtained in this embodiment are shown in Table 2.

[0059] Comparative Example 1

[0060] This comparative example refers to Example 2 in "A weathering steel for photovoltaic support and its production method" (CN114438411).

[0061] The chemical composition of the weathering steel for the photovoltaic support in this comparative example is shown in Table 1, with the remainder being Fe and unavoidable impurities.

[0062] The specific production process includes the following steps: smelting qualified molten steel through molten iron pretreatment, top and bottom combined blowing converter, LF refining outside the furnace, and RH vacuum degassing furnace; wherein the end point sulfur of molten iron pretreatment is 8ppm; the end point oxygen of top and bottom combined blowing converter is 380ppm; LF refining outside the furnace is used to make white slag, the white slag is kept for 21min, and Ca treatment is carried out to improve and promote the floating of inclusions, argon is used for soft stirring, and the soft stirring time is 12min; the vacuum degree of RH vacuum degassing furnace is 56pa, and the holding time is 18min; the molten steel is continuously cast into 210mm slab; the slab is heated to 1220℃, and the heating time is The rolling time is 160min to ensure sufficient solid solution of alloy elements; the TMCP process is used for rolling, the rolling temperature in the recrystallization zone is 1090℃, the total deformation rate is 74.7%, the opening temperature in the non-recrystallization zone of austenite is 965℃, the total deformation is 79.3%, and the final rolling temperature control range is 895℃ to avoid the precipitation of high-temperature pro-eutectoid ferrite; after rolling, it is quickly put into water with a cooling rate of 26℃ / s to cool to 620℃; the hot coil enters the slow cooling pit at 550℃ for slow cooling to fully release the internal stress caused by rolling deformation and phase transformation. After 48 hours, it comes out of the slow cooling pit and air cools to room temperature.

[0063] The specific properties of the weathering steel for photovoltaic support obtained in this comparative example are shown in Table 2.

[0064] Comparative Example 2

[0065] This comparative example refers to Example 2 in "A rare earth weathering steel for photovoltaic support and its production method" (CN115747644A).

[0066] The chemical composition of the rare earth weathering steel for the photovoltaic support in this comparative example is shown in Table 1, with the remainder being Fe and unavoidable impurities.

[0067] The specific production process includes the following steps: pre-treatment of molten iron with desulfurization, dephosphorization and decarburization of molten iron to obtain molten steel by top and bottom combined blowing converter smelting, argon blowing during converter smelting, scrap steel added to converter, and converter tapping temperature of 1630℃. Then, LF refining is performed on the molten steel after converter smelting, and the refining temperature is ≥1560℃. LF refining is performed for temperature measurement and composition fine-tuning; the overheat degree of slab continuous casting is 20℃, followed by slab cleaning, slow cooling, and continuous casting billet quality inspection; the slab heating temperature is 1130℃, the heating time is 203min, and a 7-stand continuous rolling mill is used for rolling; the finishing rolling temperature is 880℃, and the finished product thickness is 2.5mm. Laminar cooling adopts front dispersion cooling, the cooling rate is 27℃ / s, and the steel strip temperature is reduced to 633℃ for coiling.

[0068] The specific properties of the rare earth weathering steel for photovoltaic bracket obtained in this comparative example are shown in Table 2.

[0069] Table 1 Chemical composition of the embodiments and comparative examples / wt%

[0070] category C Si Mn P S Cr Ni Cu Example 1 0.07 0.39 0.49 0.073 0.004 1.14 — 0.27 Embodiment 2, 3 0.07 0.38 0.48 0.072 0.005 1.12 — 0.27 Comparative Example 1 0.043 0.35 0.86 0.014 ≤0.001 0.52 0.15 0.37 Comparative Example 2 0.08 0.35 0.95 0.012 0.005 0.50 0.08 0.23 category Nb Ti Als Alt N Ca La I Example 1 — — 0.049 — — — — 7.8 Embodiment 2, 3 — — 0.037 — — — — 7.7 Comparative Example 1 0.028 0.012 — — 0.0051 0.0017 — 6.6 Comparative Example 2 — 0.028 — 0.033 — — 18ppm 5.7

[0071] Table 2 Performance test results of embodiments and comparative examples

[0072]

[0073] Note: a indicates the relative corrosion rate of Q355B (Q345B); b indicates that the uniform corrosion thinning on both sides does not exceed 0.2mm within a 25-year service life under C1-C3 environment.

[0074] According to the chemical composition in Table 1 and the performance test results of the embodiments and comparative examples obtained in Table 2, it can be seen that: the Mn element content of the comparative example is relatively high and Ni, Nb, and Ti elements are added, which increases the alloy cost; and the comparative example adds the precious metal element Ni, but the atmospheric corrosion resistance index I is low, so the corrosion resistance of the product is relatively poor; according to the embodiments produced by the alloy composition and key process parameters provided by the present invention, the alloy composition and production method are simple, the product has excellent corrosion resistance, and has good application prospects.

Claims

A method for preparing a 1.355MPa grade hot-rolled weathering steel plate for a photovoltaic support, characterized in that: The 355MPa grade hot-rolled weathering steel plate for photovoltaic brackets comprises the following components by weight percentage: C 0.06-0.09%, Si 0.35-0.45%, Mn 0.45-0.55%, P 0.070-0.080%, S≤0.008%, Cr 1.10-1.20%, Cu 0.25-0.35%, Als 0.020-0.060%, and the balance is Fe and unavoidable impurities; The preparation method comprises the following steps: smelting the required components into slabs, and then sequentially heating, rough rolling, finish rolling, laminar cooling and coiling the slabs to obtain the slabs.

2. The method for preparing a 355MPa grade hot-rolled weathering steel plate for a photovoltaic support according to claim 1, characterized in that: The thickness of the 355MPa grade hot-rolled weathering steel plate for photovoltaic support is 1.5 to 6.0 mm.

3. The method for preparing a 355MPa grade hot-rolled weathering steel plate for a photovoltaic support according to claim 1, characterized in that: In the heating step, the slab is hot transported and hot loaded, the heating temperature is 1220-1260°C, and the heating time is 130-230 minutes.

4. The method for preparing a 355MPa grade hot-rolled weathering steel plate for a photovoltaic support according to claim 1, characterized in that: In the rough rolling step, after 6 rough rolling passes, the deformation amount of each pass is ≥18%; when the thickness of the finished hot-rolled weathering steel plate is 1.5mm≤thickness<2.5mm, the thickness of the intermediate billet is controlled to be 30-34mm; when the thickness of the finished hot-rolled weathering steel plate is 2.5mm≤thickness<4.0mm, the thickness of the intermediate billet is controlled to be 32-36mm; when the thickness of the finished hot-rolled weathering steel plate is 4.0-6.0mm, the thickness of the intermediate billet is controlled to be 40-44mm.

5. The method for preparing a 355MPa grade hot-rolled weathering steel plate for a photovoltaic support according to claim 1, characterized in that: In the finishing step, after 7 passes of finishing rolling, the reduction rates of the last three stands are ≥15%, ≥13% and ≥10% respectively, and the final rolling temperature is 860-900°C.

6. The method for preparing a 355MPa grade hot-rolled weathering steel plate for a photovoltaic support according to claim 1, characterized in that: In the laminar cooling step, the front cooling mode is adopted, and the cooling rate is ≥40°C / s.

7. The method for preparing a 355MPa grade hot-rolled weathering steel plate for photovoltaic support according to any one of claims 1 to 6, characterized in that: In the coiling step, the coiling temperature is 580 to 620°C. 8.355MPa grade hot-rolled weathering steel plate for photovoltaic bracket, characterized by: The preparation method is described in any one of claims 1 to 7.

9. The 355MPa grade hot-rolled weathering steel plate for photovoltaic support according to claim 8, characterized in that: Its yield strength is ≥355MPa, tensile strength is ≥490MPa, elongation after fracture is ≥25%, and 180° bending test D=a.

10. The 355MPa grade hot-rolled weathering steel plate for photovoltaic support according to claim 8 or 9, characterized in that: Its atmospheric corrosion resistance index I≥7.5, the relative corrosion rate of Q355B ≤35%, and the uniform corrosion thinning on both sides does not exceed 0.2mm during the 25-year service life under C1-C3 environment.

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