Coating-free low-cost high-strength weather-resistant steel plate for photovoltaic support and preparation method of high-strength weather-resistant steel plate

Abstract

The invention discloses a high-strength weather-resistant steel plate for a coating-free low-cost photovoltaic support and a preparation method of the high-strength weather-resistant steel plate. The weather-resistant steel plate is prepared from chemical components in percentage by mass as follows: 0.06%-0.09% of C, 0.25%-0.35% of Si, 1.25%-1.35% of Mn, 0.08%-0.11% of P, smaller than or equal to 0.005% of S, 0.02%-0.04% of Al, 1.05%-1.15% of Cr, 0.25%-0.35% of Cu, 0.08%-0.10% of Ti, smaller than or equal to 0.006% of N and the balance of Fe and inevitable impurities. Through the synergistic effect of alloy elements such as Cr, P and Cu, Ti microalloying and controlled rolling and controlled cooling processes are adopted for preparation, the yield strength is larger than or equal to 550 MPa, the tensile strength is larger than or equal to 600 MPa, the ductility is larger than or equal to 22%, performance is stable, weather resistance is excellent, and the requirements of photovoltaic users for high strengthening, light weight and greenization are met.

Description

Technical Field

[0001] This invention belongs to the field of weathering steel plate technology, specifically relating to a high-strength weathering steel plate for photovoltaic brackets that requires no coating and has a low cost, as well as its preparation method. Background Technology

[0002] Photovoltaic (PV) mounting systems are crucial supporting and protective structures for solar photovoltaic (PV) power generation equipment. Their most important characteristic is the need for strong corrosion resistance, ensuring the steel structure remains robust and reliable for 25 years, and withstanding harsh environmental erosion. Currently, the most commonly used materials for PV mounting systems are hot-dip galvanized or zinc-aluminum-magnesium steel components such as Q235B or Q355B. However, hot-dip galvanized or zinc-aluminum-magnesium steel supports have relatively low strength, reducing their safety. Furthermore, the hot-dip galvanizing or zinc-aluminum-magnesium steel processes cause severe environmental pollution, are costly, and have long production cycles, thus limiting their application.

[0003] To meet the photovoltaic industry's new requirements for high-strength, lightweight, green, and highly corrosion-resistant photovoltaic (PV) brackets, and to ensure reliable service in harsh environments, high-strength, high-corrosion-resistant weathering steel has come into focus for PV users. The application of weathering steel in PV brackets can be customized to require less or no coating depending on the actual service environment, thereby reducing painting and maintenance processes, environmental pollution, and extending the lifespan of the PV brackets. Furthermore, through Ti microalloying technology combined with controlled rolling and cooling processes, weathering steel can achieve high strength and excellent toughness and plasticity, allowing for material thinning while maintaining the structural rigidity and safety of the PV bracket. Therefore, the application of high-strength weathering steel in PV brackets can effectively reduce the amount of steel used, transportation costs, construction time, and painting and maintenance costs, becoming a major development direction for PV bracket materials.

[0004] Search results:

[0005] Chinese patent CN116732419A discloses "a method for producing high weather-resistant, paint-free photovoltaic bracket steel". The composition of the high weather-resistant, paint-free photovoltaic bracket steel is designed as follows: C: 0.06-0.08%, Si: 0.30-0.40%, Mn: 0.45-0.55%, P≤0.020%, S≤0.001%, Cu: 0.26-0.36%, Cr: 0.35-0.45%, Ni: 0.10-0.14%, Ti: 0.015-0.025%, La: 30-90ppm, with the balance being Fe and unavoidable impurities. This invention adopts a conventional C-Si-Mn composition system design and improves the corrosion resistance of steel by adding corrosion-resistant elements Cu, Cr, Ni and a small amount of rare earth La, thus obtaining a high weather-resistant, paint-free photovoltaic bracket steel; however, its yield strength is only about 450MPa and its tensile strength is only about 500MPa, which cannot meet the needs of high-strength photovoltaic users, and Ni and rare earth La are relatively expensive.

[0006] Chinese patent CN119392116A discloses "Weathering steel for uncoated photovoltaic brackets and its preparation method, and uncoated photovoltaic brackets." The weathering steel is designed with the following composition: C: 0.07–0.09%, Si: 0.20–0.30%, Mn: 1.0–1.1%, P: 0.07–0.09%, S≤0.003%, Cu: 0.23–0.28%, Cr: 1.0–1.1%, Mo: 0.12–0.16%, Ti: 0.040–0.065%, Al: 0.55–0.65%, Sb: 0.08–0.12%, with the balance being Fe and unavoidable impurities. Although the weathering steel obtained by this invention has a yield strength ≥550 MPa and a tensile strength ≥600 MPa, meeting the performance requirements of high-strength weathering steel, this invention adds relatively expensive Mo and Sb elements and requires RH vacuum treatment, resulting in high alloy and process costs.

[0007] The above technologies suffer from problems such as low steel strength, high alloy cost, and complex processes, and do not meet the requirements of short process, high strength, low cost, and lightweight. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a paint-free, low-cost high-strength weather-resistant steel plate for photovoltaic brackets and its preparation method. Through the synergistic effect of alloying elements such as Cr, P, and Cu, and employing Ti micro-alloying technology and controlled rolling and cooling processes, a high-strength, paint-free hot-rolled weather-resistant steel is prepared. This steel exhibits a yield strength ≥550MPa, tensile strength ≥600MPa, elongation ≥22%, and a product thickness of 2.0mm–6.0mm. It also demonstrates stable performance and excellent weather resistance, meeting the demands of photovoltaic users for high strength, lightweight, and environmentally friendly materials.

[0009] The technical solution adopted in this invention is as follows:

[0010] This invention provides a high-strength weather-resistant steel plate for photovoltaic brackets that requires no coating and has a low cost. The plate is composed of the following chemical composition by mass percentage: C: 0.06-0.09%, Si: 0.25-0.35%, Mn: 1.25-1.35%, P: 0.08-0.11%, S: ≤0.005%, Al: 0.02-0.04%, Cr: 1.05-1.15%, Cu: 0.25-0.35%, Ti: 0.08-0.10%, N: ≤0.006%, with the remainder being Fe and unavoidable impurities.

[0011] The metallographic structure of the high-strength weathering steel plate for the uncoated, low-cost photovoltaic bracket consists of polygonal ferrite and bainite, with a grain size of 10-12. The volume fraction of polygonal ferrite is 75-80%, and the volume fraction of bainite is 20-25%. The presence of a large amount of polygonal ferrite improves the plasticity of the weathering steel, ensuring its cold bending performance; while a certain proportion of bainite improves its strength, meeting the demands of photovoltaic users for high strength and lightweight construction.

[0012] The high-strength weather-resistant steel plate for the uncoated, low-cost photovoltaic bracket has a yield strength ≥550MPa, tensile strength ≥600MPa, and elongation ≥22%; it passes the 180° bending test with D=2a.

[0013] The high-strength weather-resistant steel plate used for the uncoated, low-cost photovoltaic bracket has an atmospheric corrosion resistance index (I) ≥ 8.0 and an average corrosion rate ≤ 1.35 g / m³. 2 •h, the corrosion rate relative to Q355B is ≤36.8%.

[0014] This invention also provides a method for preparing the high-strength weather-resistant steel plate for the uncoated, low-cost photovoltaic bracket, the method comprising the following steps:

[0015] (1) Desulfurization of molten iron;

[0016] (2) Converter smelting;

[0017] (3) LF furnace refining;

[0018] (4) Slab continuous casting;

[0019] (5) Slab heating;

[0020] (6) Slab rolling;

[0021] (7) Cooling and winding.

[0022] In the hot metal desulfurization step, hot metal with sulfur content ≤0.03% can be directly fed into the furnace; hot metal with sulfur content greater than 0.03% must be desulfurized, and the desulfurized hot metal [S] should be ≤0.015%.

[0023] In the converter smelting process, the converter bottom blowing adopts argon blowing mode for smelting, and slag is blocked by a slide plate and slag plug (ball) for tapping. The alloy is added starting from 1 / 4 of the tapped steel. Copper plate is added as an alloy in the scrap hopper or after tapping the converter steel. The tapping time is ≥3min.

[0024] In the LF furnace refining step, white slag refining is carried out, and the white slag holding time is ≥10min. Ferromanganese, copper plate, and ferrochrome alloy are added in place in the early stage of LF refining. 200-300m of pure calcium wire is fed into the casting furnace, and 100-300m of pure calcium wire is fed into the continuous casting furnace. The soft blowing time after feeding the wire is ≥10min.

[0025] In the slab continuous casting step, electromagnetic stirring and dynamic light pressure are used, and a chamfered crystallizer is used for production. The slab casting speed is controlled at 1.15 to 1.35 m / min.

[0026] In the slab heating step, the slab is hot-charged and heated at a temperature of 1200–1250℃ for 150–190 minutes. The actual heating temperature of 1200–1250℃ is to ensure sufficient austenitization of the slab, especially homogenization of its composition; and to ensure that the TiC precipitated during continuous casting is fully dissolved into the matrix, which is beneficial for inhibiting austenite recrystallization and grain growth during roughing and finishing rolling. The heating time of 25–35 minutes is mainly to ensure uniform and consistent temperature between the slab surface and core.

[0027] In the slab rolling process, the roughing rolling start temperature is controlled at 1120–1150℃, and the roughing rolling finish temperature is controlled at 1020–1060℃; the finishing rolling start temperature is 1000–1040℃, and the finishing rolling finish temperature is 880–920℃. The finishing rolling stage ensures the sufficient precipitation of second phases such as TiC and Ti(C,N), while controlling the ferrite ratio to improve the steel's strength, toughness, and formability. If the finishing rolling temperature is too low, the mill load is high, and the microstructure strength is uneven, which is detrimental to slab shape control; if the finishing rolling temperature is too high, partial recrystallization rolling is likely to occur, leading to mixed crystal phenomena and poor toughness and formability of the steel.

[0028] Furthermore, the cumulative reduction rate in rough rolling is ≥80%, ensuring that the slab undergoes multiple rolling passes in the austenite recrystallization zone, promoting repeated recovery and recrystallization of deformed austenite grains, and refining the austenite grain size.

[0029] Furthermore, when the finished product thickness of the high-strength weathering steel plate for uncoated low-cost photovoltaic brackets is <4.0mm (≤2.0mm), the thickness of the intermediate billet is 36-40mm; when the finished product thickness is ≤6.0mm (≤4.0mm), the thickness of the intermediate billet is 40-44mm.

[0030] In the cooling and coiling steps, laminar flow cooling employs 100% cooling at the front end, with a cooling rate of 25–35 °C / s; the coiling temperature is 560–600 °C, and after coiling, the coil is cooled in a slow cooling pit for 48 hours before being removed from storage. The optimal precipitation temperature range for TiC is 560–600 °C. Within this temperature range, fine and dispersed TiC and Ti(C,N) second-phase particles can precipitate in the matrix, playing a precipitation strengthening role and improving the strength of the steel coil. If the coiling temperature is too high, the number of second-phase precipitated particles decreases, and the grain size becomes coarse, resulting in lower steel coil strength and failing to meet the safety requirements of the structural components. If the coiling temperature is too low, bainitic structure is easily obtained, resulting in higher steel coil strength, which is detrimental to steel coil processing equipment, leads to lower elongation, and makes the steel coil prone to cracking during processing. Therefore, this invention controls the optimal coiling temperature to be 560–600 °C. After being coiled, the steel coil is cooled in a slow cooling pit for 48 hours before being taken out of the warehouse. This process has several advantages: First, it promotes the precipitation of the ε phase of Cu in weathering steel, which plays a role in age-strengthening and further improves the strength of the steel coil. Second, it ensures that the precipitated phases such as TiC are evenly distributed, stabilizes the microstructure, and reduces performance fluctuations. Third, it allows the steel coil to undergo self-tempering, eliminating the internal stress of the steel coil.

[0031] The functions and controls of each chemical component in the high-strength weather-resistant steel plate for uncoated, low-cost photovoltaic brackets provided by this invention are as follows:

[0032] C: Carbon mainly plays a solid solution strengthening role in steel, which has a great influence on the strength of steel. It is the most economical and effective element to improve the strength of steel. However, excessive carbon will form more coarse and brittle carbide particles in steel, which is detrimental to toughness, plasticity and weldability. At the same time, it will form segregation bands in the center of the steel plate, which is detrimental to bending performance and formability. Moreover, if the carbon content exceeds 0.10%, peritectic reaction is likely to occur in the steelmaking process, resulting in large fluctuations in the molten steel level. Therefore, the carbon content in this invention is controlled at 0.06 to 0.09%.

[0033] Si: Silicon mainly plays a solid solution strengthening role in steel. It is also a commonly used deoxidizing element. When used in combination with Cr, Cu, etc., it can improve the weather resistance of steel. However, excessive silicon content makes dephosphorization difficult during hot rolling and reduces the weldability of steel. Therefore, the silicon content in this invention is controlled at 0.25-0.35%.

[0034] Mn: Manganese is an important solid solution strengthening element in steel, which can significantly improve the strength and toughness of steel. However, excessive manganese content will not only increase the cost of steel, but also increase the hardenability of steel, leading to the deterioration of the weldability and the toughness of the weld heat-affected zone. At the same time, Mn is an element that is prone to segregation, which increases the non-uniformity of the microstructure. Therefore, the manganese content in this invention is controlled at 1.25 to 1.35%.

[0035] P: Phosphorus can significantly improve the atmospheric corrosion resistance of steel, but excessive phosphorus content can easily lead to segregation at grain boundaries, thereby reducing the toughness of steel, especially low-temperature impact toughness. Therefore, the phosphorus content of this invention is 0.08-0.11%.

[0036] S: Sulfur is a harmful residual element in steel, which deteriorates the corrosion resistance and toughness of steel. It also easily forms Ti4C2S2 with titanium, reducing the effective Ti content in steel and thus affecting the Ti microalloying effect. Therefore, the sulfur content in this invention is ≤0.005%.

[0037] Al: Aluminum is a commonly used deoxidizer in steel, which can fix free nitrogen in steel and improve the steel strip matrix; the dispersed AlN can inhibit the growth of austenite grains during heating and refine the grains; however, excessive Al will lead to a sharp increase in Class B inclusions in steel, resulting in a decrease in the internal quality of the steel and a reduction in the weldability and machinability of the steel strip. Therefore, the Al content in this invention is controlled at 0.02-0.04%.

[0038] Cu: Copper is the main weathering element in weathering steel, which can significantly improve the weathering performance of steel. As an alloying element, copper also plays a role in solid solution strengthening and precipitation strengthening when added to steel. However, if the copper content is too high, it is easy to cause cracks in the steel billet during heating and hot rolling, i.e., the "copper brittleness" defect, which deteriorates the surface performance of the steel billet. Therefore, the copper content in this invention is controlled at 0.25 to 0.35%.

[0039] Cr: The addition of chromium in combination with copper and nickel can enrich the steel surface and promote the formation of a dense passivation film or protective rust layer, which significantly improves the atmospheric corrosion resistance of the steel and is less expensive than copper and nickel. However, excessive chromium content will deteriorate the weldability of the steel. Therefore, the chromium content in this invention is controlled at 1.05 to 1.15%.

[0040] Titanium (Ti) is the most economical microalloying element for improving the strength of steel and is also a strong nitride-forming element. TiN formed in steel inhibits austenite grain growth during heating and suppresses recrystallized austenite grain growth during controlled rolling, thus refining the ferrite grains after phase transformation. During the coiling process after rolling, fine second-phase TiC and Ti(CN) particles precipitate, improving the steel strength through grain refinement and precipitation strengthening. Too low a titanium content results in insignificant strengthening of the steel, while too high a titanium content leads to higher steel costs. Therefore, the titanium content in this invention is controlled at 0.08–0.10%.

[0041] N: Nitrogen is an element present in the smelting process. One of the features of this invention is the use of Nb and Ti microalloying technology. Ti will react with elements such as O, N, and S in the steel. If the N content is too high, large-sized TiN will precipitate in the molten steel. This will not prevent the growth of austenite grains, nor will it play a precipitation strengthening role. On the contrary, it will reduce the fine grain strengthening and precipitation strengthening effect of titanium. Therefore, the nitrogen content of this invention is ≤0.006%.

[0042] Compared with the prior art, the present invention has the following outstanding advantages:

[0043] (1) Low alloy cost: This invention optimizes the design of alloy elements, adopts single Ti micro-alloying and low C and low S composition design, with fewer alloy types and lower content, without adding precious metals such as Ni and Nb, and Ti element is more abundant and cheaper than other micro-alloying elements, resulting in low raw material cost.

[0044] (2) Simple preparation method: The present invention has low smelting difficulty, no need for RH vacuum treatment, simple rolling process, low equipment requirements, and most steel companies can carry out production without investing in new equipment.

[0045] (3) Good surface quality: By setting reasonable heating temperature and heating time, the present invention avoids the occurrence of "copper brittleness" peeling defects in the hot rolling process, and the product surface quality is good and stable.

[0046] (4) Excellent comprehensive performance: The high-strength weather-resistant steel described in this invention has a yield strength ≥550MPa, tensile strength ≥600MPa, elongation ≥22%, excellent cold bending performance and weather resistance, can be used without coating, and has stable performance, meeting the needs of photovoltaic users for high strength, lightweight and green. Attached Figure Description

[0047] Figure 1 The microstructure is obtained after the hot-rolled plate in Example 1 is slowly cooled after being coiled. Detailed Implementation

[0048] This invention provides a high-strength weather-resistant steel plate for photovoltaic brackets that requires no coating and has a low cost. The plate is composed of the following chemical composition by mass percentage: C: 0.06-0.09%, Si: 0.25-0.35%, Mn: 1.25-1.35%, P: 0.08-0.11%, S: ≤0.005%, Al: 0.02-0.04%, Cr: 1.05-1.15%, Cu: 0.25-0.35%, Ti: 0.08-0.10%, N: ≤0.006%, with the remainder being Fe and unavoidable impurities.

[0049] The method for preparing the high-strength weather-resistant steel plate for the uncoated, low-cost photovoltaic bracket includes the following steps:

[0050] (1) Desulfurization of molten iron;

[0051] (2) Converter smelting;

[0052] (3) LF furnace refining;

[0053] (4) Slab continuous casting;

[0054] (5) Slab heating;

[0055] (6) Slab rolling;

[0056] (7) Cooling and winding.

[0057] In the hot metal desulfurization step, hot metal with sulfur content ≤0.03% can be directly fed into the furnace; hot metal with sulfur content greater than 0.03% must be desulfurized, and the desulfurized hot metal [S] should be ≤0.015%.

[0058] In the converter smelting process, the converter bottom blowing adopts argon blowing mode for smelting, and slag is blocked by a slide plate and slag plug (ball) for tapping. The alloy is added starting from 1 / 4 of the tapped steel. Copper plate is added as an alloy in the scrap hopper or after tapping the converter steel. The tapping time is ≥3min.

[0059] In the LF furnace refining step, white slag refining is carried out, and the white slag holding time is ≥10min. Ferromanganese, copper plate, and ferrochrome alloy are added in place in the early stage of LF refining. 200-300m of pure calcium wire is fed into the casting furnace, and 100-300m of pure calcium wire is fed into the continuous casting furnace. The soft blowing time after feeding the wire is ≥10min.

[0060] In the slab continuous casting step, electromagnetic stirring and dynamic light pressure are used, and a chamfered crystallizer is used for production. The slab casting speed is controlled at 1.15 to 1.35 m / min.

[0061] In the slab heating step, the slab is hot-charged and heated, the slab heating temperature is 1200-1250℃, and the furnace time is 150-190min.

[0062] In the slab rolling process, the roughing start temperature is controlled at 1120-1150℃, the roughing end temperature is controlled at 1020-1060℃, and the cumulative reduction rate of roughing is ≥80%; the finishing start temperature is 1000-1040℃, and the finishing end temperature is 880-920℃.

[0063] In the cooling and winding steps, laminar flow cooling adopts 100% cooling at the front end, with a cooling rate of 25-35℃ / s; the winding temperature is 560-600℃, and the winding is cooled in a slow cooling pit for 48 hours before being put out of storage.

[0064] The present invention will now be described in detail with reference to the embodiments.

[0065] The chemical composition and weight percentage of the steel plates in each embodiment and comparative example are shown in Table 1, with the balance being iron and unavoidable impurities.

[0066] Table 1. List of chemical composition values ​​(wt%) for the examples and comparative examples

[0067]

[0068] The main production process parameters of the steel plates in each embodiment and comparative example are shown in Table 2.

[0069] Table 2. List of main process parameters for each embodiment and comparative example of the present invention.

[0070] Note: Weathering steel SPA-H and alloy steel Q355B are commercially available products manufactured by Xinyu Iron & Steel Co., Ltd., and their production methods do not need to be described.

[0071] It should be noted that, except for Ti microalloying element, which is not within the scope of this invention, the chemical composition and rolling process of Comparative Examples 1 and 2 meet the conditions of this invention. The Ti content of Comparative Example 1 is 0.05%, lower than the Ti content of this invention. With such a low Ti content, the TiC particles precipitated during the coiling process significantly weaken the grain refinement and precipitation strengthening effect on the steel. As shown in Table 3, its yield strength is 518 MPa and tensile strength is 573 MPa, which does not meet the requirements of this invention for yield strength ≥550 MPa and tensile strength ≥600 MPa. The Ti content of Comparative Example 2 is 0.13%, higher than the Ti content of this invention. As shown in Table 3, although the Ti content increases significantly, the mechanical properties of the steel do not improve significantly, and the cost of the steel increases significantly. Therefore, the optimal range for Ti content in this invention is 0.08-0.10%. Since the mechanical properties of Comparative Example 1 do not meet the requirements and Comparative Example 2 does not meet the low-cost requirement, they are no longer included in the corrosion resistance testing experiment of this invention.

[0072] It should be further noted that, except for the heating temperature, which is outside the range of this invention, the chemical composition and rolling process of Comparative Examples 3 and 4 meet the conditions of this invention. The heating temperature of Comparative Example 3 was 1150℃, lower than the heating temperature of this invention. The lower heating temperature reduced the amount of TiC dissolved in the matrix, resulting in fewer TiC particles precipitated during the subsequent controlled rolling and cooling process. This significantly weakened the grain refinement and precipitation strengthening effects on the steel, as shown in Table 3. Its yield strength was 526 MPa and tensile strength was 578 MPa, failing to meet the requirements of this invention for yield strength ≥550 MPa and tensile strength ≥600 MPa. The heating temperature of Comparative Example 4 was 1280℃, higher than the heating temperature of this invention. As shown in Table 3, although the heating temperature increased, the mechanical properties of the steel did not improve, and the energy consumption cost of the steel increased. Therefore, the optimal heating temperature range of this invention is 1200-1250℃. Since the mechanical properties of Comparative Example 3 did not meet the requirements and Comparative Example 4 did not meet the low-cost requirement, they were not included in the corrosion resistance test of this invention.

[0073] In addition, Comparative Examples 5 and 6, except for their furnace time which is outside the scope of this invention, meet the conditions of this invention in terms of chemical composition and hot rolling process. As shown in Table 2, the furnace time of Comparative Example 5 is 120 min, which is shorter than the furnace time of this invention. The shorter furnace time reduces the amount of TiC dissolved in the matrix during heating, resulting in fewer TiC particles precipitated during the subsequent controlled rolling and cooling process. This weakens the fine grain formation and precipitation strengthening effect. As shown in Table 3, its yield strength is 521 MPa and tensile strength is 572 MPa, which does not meet the requirements of this invention (yield strength ≥ 550 MPa, tensile strength ≥ 600 MPa). Comparative Example 6 has a furnace time of 220 min, which is longer than the furnace time of this invention. Although its performance meets the requirements, the excessively long furnace time causes the slab to develop a "copper brittleness" peeling defect due to prolonged heating, failing to meet user requirements. Therefore, the optimal furnace time range for this invention is 150-190 min. Since the mechanical properties of Comparative Example 5 do not meet the requirements and the surface quality of Comparative Example 6 does not meet user requirements, they are no longer included in the corrosion resistance test of this invention.

[0074] Furthermore, Comparative Examples 7 and 8, except for their coiling temperatures which are outside the scope of this invention, meet the requirements of this invention in terms of chemical composition and other rolling processes. The coiling temperature of Comparative Example 7 is 500℃, lower than the coiling temperature of this invention. A low coiling temperature results in the formation of a large amount of bainite in the microstructure, leading to high steel strength, which is detrimental to equipment during processing, and lower plasticity and toughness, making the material prone to cracking during processing. The coiling temperature of Comparative Example 8 is 650℃, higher than the coiling temperature of this invention. A high coiling temperature results in coarse grains and larger TiC particles, weakening the fine grain formation and precipitation strengthening effect, leading to lower steel strength. As shown in Table 3, its yield strength is only 532 MPa and its tensile strength is only 585 MPa, which cannot meet the high-strength performance requirements of the next-generation photovoltaic bracket. Therefore, the optimal coiling temperature range of this invention is 560–600℃. Since the mechanical properties of Comparative Examples 7 and 8 do not meet the requirements, they are no longer included in the corrosion resistance testing experiment of this invention.

[0075] The mechanical and corrosion performance test results of the steel plates in each embodiment and comparative example are shown in Tables 3 and 4. The mechanical properties were tested according to GB / T 228 Metallic Materials Tensile Testing Method, and the corrosion performance was tested according to TB / T 2375-1993 Railway Weathering Steel Cyclic Immersion Corrosion Test Method.

[0076] Table 3. List of mechanical property test results for each embodiment and comparative example of the present invention.

[0077]

[0078]

[0079] Table 4. List of corrosion resistance test results for various embodiments of the present invention and comparative products.

[0080]

[0081] As can be seen from Tables 3 and 4, the hot-rolled weathering steel produced by this invention has a yield strength ≥550MPa, tensile strength ≥600MPa, elongation ≥22%, good cold bending and corrosion resistance, and can be used without coating, meeting the needs of photovoltaic users for high strength, lightweight and green.

[0082] The above detailed description of a high-strength weather-resistant steel plate for a low-cost, paint-free photovoltaic bracket and its preparation method is illustrative rather than limiting. Several embodiments can be listed within the defined scope. Therefore, variations and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A high-strength weathering steel sheet for a painted-free low-cost photovoltaic support, characterized in that: The said low-cost high-strength weathering steel plate for non-painting photovoltaic support is composed of the following chemical components in percentage by mass: C: 0.06-0.09%, Si: 0.25-0.35%, Mn: 1.25-1.35%, P: 0.08-0.11%, S: ≤0.005%, Al: 0.02-0.04%, Cr: 1.05-1.15%, Cu: 0.25-0.35%, Ti: 0.08-0.10%, N: ≤0.006%, and the rest is Fe and inevitable impurities. The said low-cost high-strength weathering steel plate for non-painting photovoltaic support has a metallographic structure of polygonal ferrite and bainite, and a grain size of 10-12 grade.

2. The high-strength weathering steel sheet for a painted-free low-cost photovoltaic support rack according to claim 1, characterized by: The said low-cost high-strength weathering steel plate for non-painting photovoltaic support has a yield strength of ≥550 MPa, a tensile strength of ≥600 MPa, and an elongation of ≥22%; and the 180° bending test D=2a is qualified.

3. The high-strength weathering steel sheet for a painted-free low-cost photovoltaic support rack according to claim 1, characterized by: The said preparation method comprises the following steps:

4. The high strength weathering steel sheet for a painted-less low cost photovoltaic rack according to claim 1, characterized by: The atmospheric corrosion resistance index I of the said low-cost, paint-free, high-strength, weather-resistant steel plate for photovoltaic support is greater than or equal to 8.0, and the average corrosion rate is less than or equal to 1.35 g / m 2 · h, relative Q355B corrosion rate is less than or equal to 36.8%.

5. A method of producing a high-strength weathering steel sheet for a paintless low-cost photovoltaic support according to any one of claims 1 to 4, characterized in that, (1) hot metal desulphurization; (2) converter smelting; (3) LF furnace refining; (4) slab continuous casting; (5) slab heating; (6) slab rolling; (7) cooling and coiling. In the said slab heating step, the slab is hot sent and hot charged, the slab heating temperature is 1200-1250℃, and the furnace time is 150-190 min.

6. The preparation method according to claim 5, characterized in that, In the said slab rolling step, the rough rolling starting temperature is controlled at 1120-1150℃, the rough rolling ending temperature is controlled at 1020-1060℃, the finish rolling starting temperature is 1000-1040℃, and the finish rolling ending temperature is 880-920℃.

7. The preparation method according to claim 5, characterized in that, The cumulative reduction rate of rough rolling is ≥80%.

8. The preparation method according to claim 7, characterized in that, When the finished product thickness of the said low-cost high-strength weathering steel plate for non-painting photovoltaic support is 2.0 mm≤≤4.0 mm, the intermediate slab thickness is 36-40 mm; and when the finished product thickness is 4.0 mm≤≤6.0 mm, the intermediate slab thickness is 40-44 mm.

9. The production method according to claim 5 or 7, characterized by, In the said cooling and coiling step, the laminar flow cooling uses 100% cooling in the front section, the cooling speed is 25-35℃ / s, the coiling temperature is 560-600℃, and the coiling is slowly cooled in the pit for 48 h before being discharged.

10. The method of claim 5, wherein, ​

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