Weathering steel for photovoltaic support and method for manufacturing the same

Abstract

The application relates to the field of steel smelting and rolling technology, in particular to a weather-resistant steel for a photovoltaic support and a preparation method thereof. The weather-resistant steel comprises the following chemical components: C, Si, Mn, P, S, Al, Ti, Ni, Cu, Cr, N, Ca and Fe; wherein the content of C is 0.018 wt% to 0.028 wt%, the content of Si is less than or equal to 0.015 wt%, the content of Mn is 0.10 wt% to 0.25 wt%; the content of P is 0.025 wt% to 0.065 wt%, the content of S is less than or equal to 0.003 wt%, the content of Al is 0.025 wt% to 0.05 wt%, the content of Ti is 0.035 wt% to 0.075 wt%, the content of Ni is 0.10 wt% to 0.30 wt%, the content of Cu is 0.25 wt% to 0.55 wt%; the content of Cr is 1.6 wt% to 2.6 wt%, the content of N is less than or equal to 0.0040 wt%, the content of Ca is 0.001 wt% to 0.004 wt%; and meanwhile, the following conditions are met: a weather resistance index I is greater than or equal to 8.0%, a [C] / [P] is greater than or equal to 0.4, and a [Ca] / [S] is 1.0 to 2.5. The application solves the technical problem that the existing weather-resistant steel for a photovoltaic support cannot simultaneously have high strength, high weather resistance and high cold workability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel smelting and rolling, and particularly relates to a weather-resistant steel for a photovoltaic support and a preparation method thereof. BACKGROUND

[0002] With the increasingly serious global pollution, the development of green energy is paid more and more attention by countries around the world. As a clean energy, photovoltaic power generation has been rapidly developed in China. The photovoltaic support is a supporting device for placing, installing and fixing the solar panel of the photovoltaic power generation system. The photovoltaic support is mostly located in open slopes, deserts and other places and needs to withstand the impact of strong wind, rain and snow and other bad weather. Therefore, the photovoltaic support has high requirements on strength, rigidity, plasticity, toughness, weather resistance and other properties. At present, the most widely used photovoltaic support in China is a steel support which has stable performance, mature manufacturing process, high bearing capacity and simple installation and is widely used in civil, industrial solar photovoltaic and solar power stations. The material of the steel support is generally plain carbon steel Q235 and Q355 and the surface of the steel support is treated by hot galvanizing to ensure that the steel support does not rust for 30 years of outdoor use.

[0003] At present, how to balance high strength, high weather resistance and high cold workability of the weather-resistant steel for the photovoltaic support is an urgent problem to be solved. SUMMARY

[0004] The present application provides a weather-resistant steel for a photovoltaic support and a preparation method thereof to solve the technical problem that the existing weather-resistant steel for a photovoltaic support cannot simultaneously have high strength, high weather resistance and high cold workability.

[0005] In a first aspect, the present application provides a weather-resistant steel for a photovoltaic support, and the chemical composition of the weather-resistant steel comprises:

[0006] C, Si, Mn, P, S, Al, Ti, Ni, Cu, Cr, N, Ca and Fe; wherein,

[0007] The content of C is 0.018wt%-0.028wt%, the content of Si is ≤0.015wt%, the content of Mn is 0.10wt%-0.25wt%; the content of P is 0.025wt%-0.065wt%, the content of S is ≤0.003wt%, the content of Al is 0.025wt%-0.05wt%, the content of Ti is 0.035wt%-0.075wt%, the content of Ni is 0.10wt%-0.30wt%, the content of Cu is 0.25wt%-0.55wt%; the content of Cr is 1.6wt%-2.6wt%, the content of N is ≤0.0040wt%, the content of Ca is 0.001wt%-0.004wt%;

[0008] and simultaneously satisfy: weather resistance index I≥8.0%, [C] / [P]≥0.4, [Ca] / [S] is 1.0-2.5;

[0009] [C] represents the weight of C, [P] represents the weight of P, [Ca] represents the weight of Ca, and [S] represents the weight of S.

[0010] Optionally, the metallographic structure of the weathering steel is ferrite.

[0011] In a second aspect, the present application provides a preparation method of the weathering steel for photovoltaic support, to realize the weathering steel in any one of the embodiments of the first aspect, and the method comprises:

[0012] The slab is heated so that the heated slab has a target temperature;

[0013] The heated slab is finish-rolled under the condition of a set finish rolling temperature to obtain a hot-rolled plate;

[0014] The hot-rolled plate is cooled; wherein the cooling comprises ultra-fast cooling, and the outlet temperature of the ultra-fast cooling is controlled;

[0015] The cooled hot-rolled plate is coiled under the condition of a set temperature to obtain the weathering steel for photovoltaic support.

[0016] Optionally, the target temperature is 1160-1210°C.

[0017] Optionally, the set finish rolling temperature is 880-940°C.

[0018] Optionally, the outlet temperature of the ultra-fast cooling is 670-710°C.

[0019] Optionally, the set temperature is 580-640°C.

[0020] Optionally, before the heated slab is finish-rolled under the condition of a set finish rolling temperature to obtain a hot-rolled plate, the method further comprises:

[0021] The heated slab is rough-rolled under the condition of a set rolling outlet temperature, and then cooled.

[0022] Optionally, the set rolling outlet temperature is 1100-1150°C, and / or the end temperature of the cooling is 1000-1050°C.

[0023] Optionally, the cooling of the hot-rolled plate comprises ultra-fast cooling, and the outlet temperature of the ultra-fast cooling is controlled, comprising:

[0024] The hot-rolled plate is subjected to ultra-fast cooling, and the outlet temperature of the ultra-fast cooling is controlled;

[0025] The hot-rolled plate after ultra-fast cooling is subjected to air cooling and then laminar cooling; wherein the laminar cooling adopts a sparse cooling mode of upper 2 and lower 2.

[0026] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0027] The weathering steel for photovoltaic support provided by the embodiment of the present application adopts a low-carbon-low-silicon-low-manganese basic component design, and through reasonable matching of weathering elements such as phosphorus, copper, chromium and nickel, the weathering index is strictly controlled to be greater than or equal to 8.0%, C / P is greater than or equal to 0.4, and Ca / S is 1.0-2.5. Not only the shortcomings of general carbon steel, such as environmental pollution, high price, thick specification, poor low-temperature toughness and fatigue resistance, and the defects of high-strength weathering steel, such as low plasticity, easy cracking and large springback during rolling, are avoided, but also the technical effects of yield strength of the strip steel reaching more than 550 MPa, tensile strength reaching more than 750 MPa, yield strength ratio being less than or equal to 0.75, elongation being more than 23%, corrosion rate being less than or equal to 20% of ordinary structural steel Q345B, excellent plate shape and surface quality, good cold formability and corrosion resistance are achieved, so as to meet the technical effects of processing and use performance requirements of the steel for photovoltaic support. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained based on these drawings without creative labor.

[0030] Figure 1 A flowchart of a preparation method of the weathering steel for photovoltaic support provided by the embodiment of the present application is shown.

[0031] Figure 2 A microstructure diagram of the weathering steel for photovoltaic support provided by the embodiment of the present application is shown. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will be combined with the accompanying drawings for the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0033] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present application; therefore, it should be considered that the described range has been specifically disclosed all possible sub-ranges and single values in the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers in the range, such as 1, 2, 3, 4, 5 and 6, which applies to any range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) in the indicated range.

[0034] In the present application, the orientation words such as "upper" and "lower" are specific to the drawing direction in the drawings. In addition, in the description of the specification, the terms "include", "contain" and the like mean "include but not limited to". In this document, the relationship terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. In this document, "and / or" describes the relationship between the associated objects, which means that there can be three relationships, for example, A and / or B can represent the cases of A alone, A and B together, and B alone. Where A and B can be singular or plural. In this document, "one or more" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of the items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0035] Unless otherwise specifically stated, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0036] Synergistic control of high strength, high cold workability and high weather resistance is the core technical problem solved by the present application. In order to realize high workability and high weather resistance, it is necessary to ensure low carbon content and uniform ferrite structure, but low C content and high strength are in conflict with each other; in order to realize high weather resistance, it is necessary to add high weather resistance elements such as Cu, Cr, Ni, P, etc., and high alloy element addition is not conducive to weldability and cold forming performance, especially the addition of P easily causes cracking problem due to segregation at grain boundaries; how to balance high strength, high formability and high weather resistance is the key core. Therefore, the embodiments of the present application adopt low-carbon-low-silicon-low-manganese basic component design, through reasonable proportioning of weather resistance elements such as phosphorus, copper, chromium, nickel, etc., strictly control the weather resistance index ≥8.0%, C / P ≥0.4, Ca / S = 1.0-2.5, combined with low-temperature discharge, high-temperature finishing, high-temperature coiling and ultra-fast cooling hot rolling process system, to obtain hot-rolled strip steel with excellent cold formability, weldability and weather resistance, to avoid cracking problems, size precision problems, iron oxide scale shedding problems and welding cold cracks in the processing of photovoltaic support steel, to meet the demand of high strength and high weather resistance of photovoltaic support steel. Through the above product composition and process design, the technical problems of existing photovoltaic support weathering steel which is difficult to simultaneously consider high strength, high weather resistance and high cold workability are solved, and the disadvantages of existing technology such as environmental pollution, high price, thick specification, poor low temperature toughness, etc. of hot galvanizing of plain carbon steel are effectively avoided, realizing that the yield strength of the strip steel can reach more than 550MPa, the tensile strength can reach more than 750MPa, the yield strength ratio is ≤0.75, the elongation is more than 23%, the corrosion rate is ≤20% compared with ordinary structural steel Q345B, to meet the processing and use performance requirements of photovoltaic support steel.

[0037] In a first aspect, the present application provides a weathering steel for photovoltaic support, the chemical composition of the weathering steel comprising:

[0038] C, Si, Mn, P, S, Al, Ti, Ni, Cu, Cr, N, Ca and Fe; wherein,

[0039] The content of C is 0.018wt%-0.028wt%, the content of Si is ≤0.015wt%, the content of Mn is 0.10wt%-0.25wt%; the content of P is 0.025wt%-0.065wt%, the content of S is ≤0.003wt%, the content of Al is 0.025wt%-0.05wt%, the content of Ti is 0.035wt%-0.075wt%, the content of Ni is 0.10wt%-0.30wt%, the content of Cu is 0.25wt%-0.55wt%; the content of Cr is 1.6wt%-2.6wt%, the content of N is ≤0.0040wt%, the content of Ca is 0.001wt%-0.004wt%;

[0040] and simultaneously satisfy: weather resistance index I ≥ 8.0%, [C] / [P] ≥ 0.4, [Ca] / [S] is 1.0-2.5;

[0041] [C] represents the weight of C, [P] represents the weight of P, [Ca] represents the weight of Ca, and [S] represents the weight of S.

[0042] Hot-dip galvanizing of plain carbon steel not only produces beam wastewater and waste acid in production, causing environmental pollution, but also has long production flow, high price of raw material zinc, low strength grade, thick use specification, poor low-temperature toughness and poor fatigue resistance, and other shortcomings. Application of weathering steel to photovoltaic support can avoid the occurrence of such problems, and the rust-proof performance of the material itself can fully meet the requirements of high strength and high weather resistance. Photovoltaic support is generally hot-rolled strip steel after longitudinal cutting, and is formed into pipe or C-shaped beam of various cross-sectional sizes by roll forming, so the steel for photovoltaic support needs to have good cold forming performance; according to the service environment characteristics, the steel for photovoltaic support also needs to have high strength, high weather resistance and other properties.

[0043] Weathering steel generally adds a certain amount of P, Cu, Cr, Ni and other weather-resistant alloy elements in the steel, the purpose is to form a dense oxide film on the surface, and the air enters the matrix to further corrosion, so as to achieve the weather resistance. Compared with ordinary weathering steel, high-strength weathering steel also needs to add a certain amount of micro-alloying elements such as Nb, V, Ti and Mo in the steel, combined with controlled rolling and controlled cooling process, through precipitation strengthening and fine-grain strengthening to improve the strength, the overall yield strength ratio is high, generally above 0.9. Due to the high yield strength ratio, the springback is large during roll forming, and the size precision is difficult to guarantee; at the same time, due to the high amount of alloying elements, the plasticity and toughness are often significantly reduced, and surface cracking defects are easy to occur during roll forming; in addition, for weathering steel with high content of Mn, Si and P, segregation band is easy to form, or P is easy to segregate at grain boundary, which leads to significant reduction of cold forming performance. Therefore, for high-strength steel for high-weather photovoltaic support, the design of chemical composition and hot rolling process is extremely important.

[0044] The positive effect of controlling the content of C to be 0.018wt%-0.028wt%: C has an adverse effect on plasticity, weldability and corrosion resistance, mainly because when the content of C is high, more coarse tertiary cementite will be formed and the transformation of pearlite structure will be promoted, which leads to the increase of the inhomogeneity of the steel matrix, which is not conducive to corrosion resistance, and the cold formability, low temperature toughness and weldability of the strip steel are also reduced. From the perspective of plasticity, toughness and corrosion resistance, it is appropriate to have a lower content of C in the steel. However, when the content of C is too low, the migration speed of the austenite grain boundary is high, which is not conducive to the refinement of austenite grains, leading to the problem of coarse final structure; for high-P weathering steel, it is not easy to control the brittleness problem caused by the grain boundary segregation of P when the content of C is too low. Specifically, the content of C can be 0.018wt%, 0.020wt%, 0.022wt%, 0.024wt%, 0.026wt%, 0.028wt% and the like.

[0045] The positive effect of controlling the content of Si to be ≤0.015wt%: Si is a solid solution strengthening element that improves the strength of the steel through solid solution strengthening, but when the content of Si is high, it not only seriously segregates in the slab, which damages the low temperature toughness and weldability of the steel plate, but also forms fayalite phase, which makes it difficult to remove the scale and form strip-shaped scale defects. Specifically, the content of Si can be 0.015wt%, 0.014wt%, 0.013wt% and the like.

[0046] The positive effect of controlling the content of Mn to be 0.10wt%-0.25wt%: Mn is a solid solution strengthening element that helps to increase the strength of the steel, while expanding the austenite phase region and reducing the critical phase transition point, which refines the structure, but when the content of Mn is high, it will increase the degree of internal segregation of the steel plate, especially for steel with high P content, Mn element will greatly increase the degree of internal segregation, forming serious segregation band, which reduces plasticity and toughness and affects cold formability. When the content of Mn is too low, it is easy to lead to coarse grains or mixed crystal structure. Specifically, the content of Si can be 0.10wt%, 0.12wt%, 0.14wt%, 0.16wt%, 0.18wt%, 0.20wt%, 0.22wt%, 0.24wt% and the like.

[0047] The positive effect of controlling the content of P to be 0.025wt%-0.065wt% and [C] / [P]≥0.4: When the content of P element is low, it is mainly an impurity element in the steel, and generally speaking, the lower the content is, the better. However, P element contributes a lot to the weather resistance of the steel plate, and it is very important to add a certain amount of P element in the steel to ensure high weather resistance. However, P element is easy to cause center segregation of the steel, which seriously deteriorates the weldability and plasticity and toughness of the steel. Specifically, the content of P can be 0.025wt%, 0.030wt%, 0.035wt%, 0.040wt%, 0.045wt%, 0.050wt%, 0.055wt%, 0.060wt%, 0.065wt% and the like; the ratio of [C] / [P] can be 0.4, 0.5, 0.6 and the like.

[0048] The positive effect of controlling the content of S to be ≤0.003wt%: S element is easy to form MnS inclusions with Mn element, which will reduce the formability, fatigue performance and low temperature toughness of the steel, and should be reduced as much as possible. Specifically, the content of S can be 0.003wt%, 0.0025wt%, 0.0020wt% and the like.

[0049] The positive effect of controlling the content of Al to be 0.025wt%-0.05wt%: Al acts as a deoxidizer during steelmaking, and has the effect of combining with N element in the steel to inhibit the growth of austenite grains in the hot rolling process and refine the recrystallized grains. The steel requires good cold formability during rolling forming, and incomplete deoxidization will lead to a decrease in the cold formability of the material. In order to meet the formability requirements of the steel plate, the content of Al should be ≥0.025%. However, too high content of Al will lead to too many AlN inclusions in the steel, which will reduce the elongation and fatigue resistance of the material. Specifically, the content of Al can be 0.025wt%, 0.03wt%, 0.035wt%, 0.040wt%, 0.045wt%, 0.05wt% and the like.

[0050] The positive effect of controlling the content of Ti to be 0.035wt%-0.075wt%: Ti combines with C in the steel to form Ti carbonitride precipitates, which have a significant precipitation strengthening effect. On the other hand, Ti content should not be too high, as it will form a lot of liquid TiN, which cannot be dissolved upon heating and has a significant impact on cold formability. Specifically, the content of Ti can be 0.035wt%, 0.040wt%, 0.045wt%, 0.050wt%, 0.055wt%, 0.060wt%, 0.065wt%, 0.070wt%, 0.075wt% and the like.

[0051] The positive effect of controlling the content of Ni to be 0.10wt%-0.30wt% and the content of Cu to be 0.25wt%-0.55wt%: Ni and Cu are generally added to the steel as corrosion-resistant elements, and are generally added in combination, and their contribution to the weather resistance of the steel plate is only next to that of P element. The addition of Cu element is essential for high weather-resistant steel. Cu can form a dense α-FeOOH oxide layer on the surface of the steel, preventing further corrosion of the matrix structure of the steel. However, the addition of Cu is prone to cause copper embrittlement defects, especially for high P element content, which is prone to form low-melting-point CuxPy intermetallic compounds at the grain boundary, causing intergranular brittle fracture. Therefore, in order to inhibit copper embrittlement defects, a certain amount of Ni element is generally added, and the addition of a certain amount of Ni element can also improve the weather resistance of the steel plate. However, Ni element is a precious metal element, and considering the cost, the addition amount should not be too much. When the addition amount of Cu is less than or equal to 0.25%, the high weather resistance cannot be achieved. Specifically, the content of Ni can be 0.010wt%, 0.015wt%, 0.020wt%, 0.025wt%, 0.030wt% and the like; the content of Cu can be 0.25wt%, 0.30wt%, 0.35wt%, 0.40wt%, 0.45wt%, 0.50wt%, 0.55wt% and the like.

[0052] The positive effect of controlling the content of Cr to be 1.6wt%-2.6wt%: the addition of Cr element in the steel can promote the formation of a dense amorphous oxide layer, and a certain amount of Cr element must be added in the high weather-resistant steel. The addition of Cr element can increase the hardenability of the steel, refine the ferrite grains, and at the same time, Cr element is dissolved in the matrix to improve the strength of the steel through solid solution strengthening, especially for the steel with low C and Mn element content, the addition of Cr element can significantly improve the tensile strength of the steel and promote low yield ratio. However, when the addition amount of Cr element is too high, the cold forming performance of the steel will be damaged. On the other hand, when the addition amount of Cr element is too low, the weather resistance cannot be achieved. Specifically, the content of Cr can be 1.6wt%, 1.8wt%, 2.0wt%, 2.2wt%, 2.4wt%, 2.6wt% and the like.

[0053] The positive effect of controlling the content of N to be ≤0.0040wt%: N element is an element existing in the smelting process, which needs to be controlled within a certain range. For Ti-containing steel, higher N content is prone to cause cracks in the slab and larger TiN precipitates. Specifically, the content of N can be 0.0040wt%, 0.0035wt%, 0.0038wt%, 0.0039wt% and the like.

[0054] The positive effect of controlling the content of Ca to be 0.001 wt% to 0.004 wt% and the ratio of [Ca] / [S] to be 1.0 to 2.5: Ca has the effect of making the stretched inclusions (MnS) into granular inclusions (Ca(Al)S(O)), controlling the morphology of inclusions, and improving the formability. The effect is obvious when the content is 0.001% or more, but when the content is too large, the size of Ca(O,S) is coarse, the brittleness is also increased, which can become the starting point of fracture cracks, and the low-temperature toughness and cold working properties of the steel are reduced. Specifically, the content of Ca can be 0.001 wt%, 0.002 wt%, 0.003 wt%, 0.004 wt%, etc.; the ratio of [Ca] / [S] can be 1, 1.5, 2.0, 2.5, etc.

[0055] The positive effect of controlling the corrosion resistance index I to be ≥8.0%: to ensure the corrosion resistance of the strip steel, the corrosion resistance index is limited, and according to the ASTM G 101 standard, the formula I = 26.01(Cu) + 3.88(Ni) + 1.20(Cr) + 1.49(Si) + 17.28(P) - 7.29(Cu)*(Ni) - 9.10(Ni) - 33.39(Cu) 2 is used to evaluate the atmospheric corrosion resistance of low alloy steel. The mass percentage of the above-mentioned elements is used for calculation. Specifically, the corrosion resistance index I can be 8.0%, 8.5%, 9.0%, etc.

[0056] In some embodiments, the metallographic structure of the weathering steel is ferrite, please refer to Figure 2 .

[0057] In the embodiments of the present application, the microstructure of the weathering steel is single ferrite structure, and the ferrite grain size is mainly between 2.0 μm and 8.0 μm. The ferrite contains nanoscale precipitates, and the nanoscale precipitates mainly have a particle size distribution of 1 nm to 20 nm, and the proportion is ≥80%.

[0058] In a second aspect, the present application provides a preparation method of a weathering steel for a photovoltaic support, to realize the weathering steel of any one of the embodiments of the first aspect, please refer to Figure 1 , the method comprises:

[0059] S1, heating the slab with the chemical composition so that the heated slab has a target temperature;

[0060] S2, under the condition of setting the final rolling temperature, finishing rolling the heated slab to obtain a hot-rolled plate;

[0061] S3, cooling the hot-rolled plate; wherein the cooling comprises ultrafast cooling, and the outlet temperature of the ultrafast cooling is controlled;

[0062] S4, under the condition of setting temperature, the cooled hot-rolled plate is coiled to obtain the weather-resistant steel for photovoltaic support.

[0063] The slab with the above chemical composition is combined with a hot-rolling process system of low-temperature discharge, high-temperature finishing, high-temperature coiling and ultra-fast cooling to obtain a hot-rolled strip steel with excellent cold formability, welding performance and weather resistance, so as to avoid cracking problems, poor size accuracy problems, iron oxide skin shedding problems and welding cold cracks and other defects in the processing of the steel for photovoltaic support, and meet the requirements of high strength and high weather resistance of the steel for photovoltaic support.

[0064] In some embodiments, the target temperature is 1160-1210℃.

[0065] The molten steel with the above composition is smelted by a known smelting method such as a converter, and a continuous casting billet is made by a known casting method such as a continuous casting method. The hot-rolling process is performed on the continuous casting billet to make a hot-rolled strip steel. The heating temperature of the continuous casting billet is 1160-1210℃, and the heating time is 3.0-3.5h to obtain a slab with a target temperature. The "target temperature" refers to the discharge temperature of the slab, and the heating temperature and time of the continuous casting billet need to consider the solid solution of micro-alloying elements and the coarsening behavior of the original austenite grains. Since the product is mainly thin gauge, Nb element is not added to consider the rolling stability of thin gauge, and Ti micro-alloying is mainly used, so the heating temperature cannot be too low, too low cannot guarantee the Ti carbonitride dissolution, and the thin gauge rolling stability is also insufficient; and the heating temperature cannot be too high, too high heating temperature will lead to the coarsening of the original austenite grains, and the final structure cannot be refined, which affects the cold formability and low temperature toughness; from the perspective of refining the final structure, the heating temperature is as low as possible. Since the heating temperature is set to be low, in order to ensure the uniformity of the structure, the heating time is slightly longer, but the heating time cannot be too long, otherwise the precipitates will be coarsened, which will also cause the coarsening of the original austenite grains. Considering the refinement of the original austenite grains, the dissolution of the micro-alloying elements and the rolling stability of the thin gauge, the system of low-temperature discharge and long-time heating is selected. Specifically, the temperature can be 1160℃, 1180℃, 1200℃, 1210℃, etc.

[0066] In some embodiments, the set finishing temperature is 880-940℃.

[0067] "set finish rolling temperature" means the finish rolling temperature of the finishing rolling process, the total compression ratio of the finishing rolling process is 80-90%, the grain is sufficiently refined by increasing the rolling reduction in the unrecrystallization zone, but the compression ratio cannot be too large, so as to avoid affecting the rolling stability of the thin gauge; the finishing rolling inlet temperature is controlled at 980-1030°C, the single pass reduction rate of the finishing rolling stages F1 and F2 is 40-45%, mainly to ensure that F1 and F2 avoid part of the recrystallization zone, the main reason is that the rolling temperature of F1 and F2 is high, if the compression ratio is large, recrystallization is easy to occur, leading to mixed crystal problem. At the same time, the rolling reduction rate of the last stand is <10%, to ensure the rolling stability and shape quality.

[0068] The positive effects of controlling the finish rolling temperature to be 880-940°C are: firstly, increasing the rolling speed in the finishing rolling zone is beneficial to ensure that F1-F7 do not occur recrystallization phenomenon; secondly, the C and Mn element contents of the steel grade are low, and the P content is high, which will lead to a higher phase change end point temperature, so a higher finish rolling temperature is needed to ensure rolling in the austenite zone and avoid the problem of mixed crystal in the austenite and ferrite dual phase zone; and the finish rolling temperature cannot be too high, so as to avoid leading to too coarse structure and being unable to guarantee the required strength grade. Specifically, the finish rolling temperature of the finishing rolling can be 880°C, 900°C, 920°C, 940°C, etc.

[0069] In some embodiments, the outlet temperature of the ultrafast cooling is 670-710°C.

[0070] The positive effects of controlling the outlet temperature of the ultrafast cooling to be 670-710°C are: firstly, the temperature after rolling is high, and rapid cooling to a suitable temperature is beneficial to obtain fine structure, and secondly, the finishing rolling end temperature is in the temperature range of inducing a large amount of Ti precipitation by phase change, and after the finishing rolling, the ultrafast cooling is beneficial to inhibit the precipitation of Ti at high temperature, so that more microalloying elements are precipitated after cooling and coiling, which is beneficial to obtain a large amount of fine and dispersed nanoscale precipitates. The design of the ultrafast cooling end temperature mainly considers the purpose of structure control and cooling uniformity, and too low outlet temperature of the ultrafast cooling will lead to large cooling stress, which is not conducive to the control of the shape; and too high ultrafast cooling temperature is in the high temperature zone of the two-phase zone, which will coarsen the proeutectoid ferrite, which is not conducive to the refinement of the structure. Specifically, the outlet temperature of the ultrafast cooling can be 670°C, 680°C, 690°C, 700°C, 710°C, etc.

[0071] In some embodiments, the set temperature is 580-640°C.

[0072] "set temperature" means the coiling temperature, and the positive effect of controlling the coiling temperature to be 580-640°C is that it is beneficial to the precipitation of Ti element and the refinement of the structure. If the coiling temperature is too low, it is not conducive to the precipitation of Ti; if the coiling temperature is too high, it is not conducive to the refinement of the structure and the second phase precipitates. After the S4 step, the hot-rolled steel is coiled above 500°C into a slow cooling pit and taken out after slow cooling for 48 hours and then air-cooled to room temperature. The purpose of slow cooling is to promote the nanoscale second phase precipitation and increase the proportional contribution of precipitation strengthening. Specifically, the coiling temperature can be 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, etc.

[0073] In some embodiments, before the hot-rolled plate is obtained by finish rolling the heated slab under the condition of setting the finish rolling temperature, the method further comprises:

[0074] The heated slab is rough-rolled under the condition of setting the rolling exit temperature, and then cooled.

[0075] In the embodiments of the present application, the rough rolling adopts a rolling process of 1+5 mode (R1 one-pass rolling, R2 five-pass rolling), and a five-pass scale removal process is implemented, i.e., R1 one-pass scale removal, R2 one-pass, two-pass, three-pass and five-pass scale removal, to ensure that the surface iron oxide scale is completely removed; the rough rolling opens one-pass, two-pass, three-pass and five-pass scale removal. The rough rolling process adopts a high-temperature large reduction system to ensure that each pass can realize recrystallization and refine the original austenite grains, and the total reduction rate of rough rolling is between 75% and 85%, and the F1 rolling reduction is ≥20%. As the rolling temperature decreases, the reduction rate gradually increases.

[0076] In some embodiments, the set rolling exit temperature is 1100-1150°C, and / or the end temperature of the cooling is 1000-1050°C.

[0077] "set rolling exit temperature" means the exit temperature of rough rolling, and the positive effect of controlling the exit temperature of rough rolling to be 1100-1150°C is that it ensures the smooth progress and efficiency of rolling. If the exit temperature of rough rolling is too low, it may enter the partial recrystallization zone; if the exit temperature of rough rolling is too high, it affects the rolling rhythm of rough rolling and is not conducive to the improvement of efficiency. Specifically, the temperature can be 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, etc.

[0078] The positive effect of controlling the end point temperature of the cooling to be 1000-1050℃ is that it is beneficial to the stability of thin gauge rolling and ensures that the microstructure of the strip is fine and uniform. If the cooling temperature is too low, it is not conducive to the stability of thin gauge rolling to some extent; if the cooling temperature is too high, it will lead to deterioration of the microstructure of the strip to some extent. Specifically, the temperature can be 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, etc.

[0079] In some embodiments, the hot-rolled plate is cooled; wherein the cooling comprises ultra-fast cooling, and the outlet temperature of the ultra-fast cooling is controlled, comprising:

[0080] The hot-rolled plate is subjected to ultra-fast cooling, and the outlet temperature of the ultra-fast cooling is controlled.

[0081] The hot-rolled plate after ultra-fast cooling is subjected to air cooling, and then subjected to laminar cooling; wherein the laminar cooling adopts a sparse cooling mode of upper 2 lower 2.

[0082] In the embodiments of the present application, the strip is subjected to air cooling after the ultra-fast cooling is completed, and is subjected to laminar cooling after air cooling for 3-5s, and the laminar cooling adopts a sparse cooling mode of upper 2 lower 2. The air cooling for 3-5s after the ultra-fast cooling is completed is conducive to the occurrence of interphase precipitation, and the interphase precipitation has good thermal stability, and a small amount of proeutectoid ferrite transformation can also occur. Because the air cooling time is short, the proeutectoid ferrite is not easy to grow, which is conducive to the refinement of the microstructure. The laminar cooling adopts a sparse cooling mode, which is conducive to the control of the shape of the plate.

[0083] The weathering steel for photovoltaic support is realized based on the preparation method of the weathering steel for photovoltaic support. The specific steps of the preparation method of the weathering steel for photovoltaic support can refer to the above embodiments. Since the weathering steel for photovoltaic support adopts part or all of the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, and will not be described here.

[0084] The present application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods not specified in the following examples are generally determined according to national standards. If there is no corresponding national standard, the international standard, the conventional condition, or the condition suggested by the manufacturer is used.

[0085] In this embodiment, the chemical component ratio is carried out, and the weathering steel for photovoltaic support is successfully prepared according to the steps of smelting→continuous casting→continuous casting blank heating→rough descaling→width setting press→rough rolling→intermediate blank cooling→flying shear→fine descaling→finish rolling→ultra-fast cooling→laminar cooling→coiling into a steel coil→slow cooling, etc.

[0086] (1) Smelting and continuous casting: smelting molten steel according to the set composition and casting into billets, the chemical elements are shown in Table 1 in terms of mass percentage content.

[0087] (2) Slab heating: the continuous casting billets are heated at 1160-1210℃ for 3.0-3.5h to fully austenitize and ensure the dissolution of micro-alloying elements, and the heating process is shown in Table 2.

[0088] (3) Hot rolling: the heated continuous casting slab is rough dephosphorized to remove the iron oxide scale on the surface of the strip, and the dephosphorized continuous casting billet is rough rolled with a reduction rate of 75-85%, and the rough rolling is opened for 1, 2, 3 and 5 passes to remove scale; the outlet temperature of the rough rolling is 1100-1150℃; the intermediate billet is rapidly cooled, and the cooling end temperature is 1000-1050℃; the intermediate slab is fine de-scaling with a pressure greater than 18MPa, and the fine de-scaling intermediate billet is fine rolled to obtain a strip, and the total compression ratio of the fine rolling is 80-90%; the fine rolling inlet temperature is controlled at 980-1030℃, the single pass reduction rate of F1 and F2 in the fine rolling stage is 40-45%, the rolling reduction rate of the last rack is <10%, and the fine rolling end temperature is 880-940℃, and the hot rolling process is shown in Table 3.

[0089] (4) Laminar cooling: the strip is super-fast cooled after fine rolling, and the super-fast cooling outlet temperature is 670-710℃; the strip is air cooled after the super-fast cooling, and the laminar cooling is carried out after 3-5s of air cooling, and the laminar cooling adopts the sparse cooling mode of upper 2 and lower 2; the laminar cooled strip is coiled to obtain a hot rolled steel coil, and the coiling temperature is 580-640℃; the hot rolled steel coil is put into the slow cooling pit for slow cooling when the temperature is above 500℃, and is taken out after 48 hours of slow cooling and air cooling to room temperature.

[0090] Table 1 lists the mass percentage content of each chemical element of the weather-resistant steel for photovoltaic support in Examples 1-4 and Comparative Examples 1-4 according to different chemical component proportions.

[0091] Table 1 Chemical composition of weather-resistant steel for photovoltaic support (wt%), the balance is Fe and other unavoidable impurities

[0092]

[0093] Table 2 lists the related process parameters for manufacturing the weather-resistant steel for photovoltaic support in Examples 1-4 and Comparative Examples 1-4.

[0094] Table 2 Process parameters for preparing weather-resistant steel for photovoltaic support

[0095]

[0096]

[0097] Table 3 lists the mechanical properties of the weathering steels for photovoltaic support racks of Examples 1-4 and Comparative Examples 1-4.

[0098] Table 3 lists the mechanical properties of the weathering steels for photovoltaic support racks of Examples 1-4 and Comparative Examples 1-4.

[0099]

[0100]

[0101] As can be seen from Table 3, the yield strength of the weathering steels for photovoltaic support racks is greater than 550 MPa, and the maximum is 590 MPa; the tensile strength is greater than 750 MPa, and the maximum is 795 MPa; the elongation is greater than or equal to 23.0%, and the maximum is 25.0%; at the same time, the 180° d = 1 a cold bending test is qualified; the corrosion rate relative to the ordinary structural steel Q345B is less than or equal to 20%; and the steel strip made of the steel has excellent cold forming performance, welding performance and corrosion resistance.

[0102] Examples 1-4 are all ferrite structures, and there is no edge buckling and red iron oxide scale on the surface of the steel strip, and the iron oxide scale does not fall off during the forming process. As can be seen from Comparative Examples 1-2, Comparative Examples 1-2 add Cu-Cr-Ni and a higher content of P to obtain high weather resistance, although the contents of C, Si and Mn are higher than those of the examples, the Cr and Ti contents are significantly lower than those of the examples, the strength index is lower, the yield strength is about 430 MPa, and the tensile strength is 560-650 MPa, the strength is lower, and it cannot meet the requirement of high strength; Comparative Example 3 adopts a composition design of low C-low Mn-low Si, and adds a higher amount of Cu, Cr and Ni elements, especially a very high amount of Cr element, to obtain high weather resistance, but too high Cr will damage the cold forming performance of the steel. However, because the P content is low, the relative corrosion rate exceeds 20%; at the same time, due to the low Ti content, the yield strength is below 500 MPa, the tensile strength is below 600 MPa, and the yield strength ratio is as high as 0.81; Comparative Example 4 adopts a higher content of C, Si, Mn and Ti elements to obtain high strength, and the yield strength is higher than 750 MPa, but the elongation is low, and the forming is at risk of cracking. In addition, the contents of P, Cu, Ni and Cr, which are weather resistance elements, are insufficient, and the relative corrosion rate is 38%, and the weather resistance is insufficient. In summary, the weathering steel for photovoltaic support racks provided by the present application solves the technical problem that the existing weathering steel for photovoltaic support racks cannot simultaneously have high strength, high weather resistance and high cold processing performance.

[0103] The foregoing detailed description of the application has been presented for purposes of illustration and description. Various modifications and changes can be made to these embodiments without departing from the spirit and scope of the application. It is intended that the scope of the application should not be limited by the particular representative embodiments described above.

Claims

1. A weathering resistant steel for a photovoltaic support, characterized in that, The chemical composition of the weather-resistant steel comprises: C, Si, Mn, P, S, Al, Ti, Ni, Cu, Cr, N, Ca, and the balance of Fe; wherein, The content of C is 0.018 wt%~0.028 wt%, the content of Si is ≤0.015 wt%, the content of Mn is 0.10 wt%~0.25 wt%; the content of P is 0.025 wt%~0.065 wt%, the content of S is ≤0.003 wt%, the content of Al is 0.025 wt%~0.05 wt%, the content of Ti is 0.035 wt%~0.075 wt%, the content of Ni is 0.10 wt%~0.30 wt%, the content of Cu is 0.25 wt%~0.55 wt%; the content of Cr is 1.6 wt%~2.6 wt%, the content of N is ≤0.0040 wt%, the content of Ca is 0.001 wt%~0.004 wt%; And simultaneously satisfy: weather resistance index I≥8.0%, [C] / [P]≥0.4, [Ca] / [S] is 1.0~2.5; [C] represents the weight of C, [P] represents the weight of P, [Ca] represents the weight of Ca, and [S] represents the weight of S; The preparation method of the weather-resistant steel comprises: Heating the slab so that the heated slab has a target temperature; Finishing rolling the heated slab under the condition of setting a finish rolling temperature to obtain a hot-rolled plate; Super-fast cooling the hot-rolled plate and controlling the outlet temperature of the super-fast cooling; Air cooling the hot-rolled plate after super-fast cooling, and after air cooling for 3-5 s, laminar cooling is performed; the laminar cooling adopts a sparse cooling mode of upper 2 lower 2; Coiling the cooled hot-rolled plate under the condition of setting a temperature to obtain a weather-resistant steel for photovoltaic support. The target temperature is 1160℃~1210℃, the finish rolling temperature is set to 880℃~940℃, the outlet temperature of the super-fast cooling is 670℃~710℃, and the setting temperature is 580℃~640℃.

2. Weathering steel according to claim 1, characterized in that The metallographic structure of the weather-resistant steel is ferrite.

3. A method for producing a weathering steel for a photovoltaic support, characterized in that, A method for preparing the weather-resistant steel of claim 1 or 2, the method comprising: Heating the slab so that the heated slab has a target temperature; Finishing rolling the heated slab under the condition of setting a finish rolling temperature to obtain a hot-rolled plate; Super-fast cooling the hot-rolled plate and controlling the outlet temperature of the super-fast cooling; Air cooling the hot-rolled plate after super-fast cooling, and after air cooling for 3-5 s, laminar cooling is performed; Coiling the cooled hot-rolled plate under the condition of setting a temperature to obtain a weather-resistant steel for photovoltaic support.

4. The method of claim 3, wherein, Before the finishing rolling of the heated slab under the condition of setting a finish rolling temperature to obtain a hot-rolled plate, the method further comprises: Coarsely rolling the heated slab under the condition of setting a rolling outlet temperature, and then cooling.

5. The method of claim 4, wherein, The setting rolling outlet temperature is 1100℃~1150℃, and the end point temperature of the cooling is 1000℃~1050℃.

Images