A weathering steel and a method for producing the same

Abstract

The application provides a weather-resistant steel and belongs to the technical field of steel smelting and rolling. The chemical components of the weather-resistant steel are as follows in mass fraction: Ni: 0.015% to 0.05%, Cu: 0.2% to 0.5%, Cr: 1.6% to 3.0%, C: less than or equal to 0.120%, and the rest is Fe and inevitable impurities. When the weather-resistant steel is applied to products such as photovoltaic supports, Cu and Cr are used in proportion to form a dense alpha-FeOOH oxidation layer on the surface of the steel, prevent the base body structure of the steel from being further corroded, and improve the corrosion resistance of the steel. The addition of Ni can inhibit the copper embrittlement defect formed due to the addition of Cu. Controlling the content of C can avoid the disadvantage of high C content on the corrosion resistance and low-temperature toughness of the steel. Therefore, the weather-resistant steel provided by the application can improve the weather resistance of the steel and can be used in photovoltaic supports, thereby solving the technical problem of short service life of the photovoltaic support.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel smelting and rolling, and particularly relates to a weathering steel and a preparation method thereof. BACKGROUND

[0002] The weathering steel is smelted by adding a small amount of corrosion-resistant elements such as copper and nickel to plain carbon steel, and is widely used in steel structures such as railways, vehicles and bridges which are exposed to the atmosphere for a long time due to its excellent corrosion resistance.

[0003] The photovoltaic support is a support designed for placing, installing and fixing solar panels in a solar photovoltaic power generation system, and is required to have strong structural strength and rigidity, good low-temperature toughness and the like, and can resist the influence of special weather such as rain and snow. At present, the material of the domestic solar photovoltaic support is mainly plain carbon steel, but it has problems such as low strength, thick specification, poor low-temperature toughness and fatigue resistance, and the existing treatment method is to perform hot galvanizing treatment on the surface of the plain carbon steel, but the galvanizing has problems such as high cost, long cycle, environmental pollution and the like, and the production quantity has gradually decreased. SUMMARY

[0004] The embodiments of the present application provide a weathering steel and a preparation method thereof to solve the technical problem of short service life of products such as photovoltaic supports.

[0005] In a first aspect, the embodiments of the present application provide a weathering steel, and the chemical composition of the steel is 0.015% to 0.05% of Ni, 0.2% to 0.5% of Cu, 1.6% to 3.0% of Cr, 0.120% or less of C, and the rest is Fe and inevitable impurities.

[0006] Further, the chemical composition of the weathering steel further includes 0.08% to 0.12% of Ti, 0.0040% or less of N, and 0.055% or more of C.

[0007] Further, the chemical composition of the weathering steel further includes 0.015% to 0.050% of Nb, 0.01% to 0.10% of V, and Nb+V+Ti≤0.20%.

[0008] Further, the chemical composition of the weathering steel further includes 1.75% to 2.20% of Mn, 0.02% to 0.05% of Al or

[0009] 1.75% to 2.20% of Mn, 0.02% to 0.05% of Al, and 0.10% or less of Si.

[0010] Further, the metallographic structure of the weathering steel comprises ferrite and pearlite, the ferrite contains nanoscale precipitates, and the volume ratio of the nanoscale precipitates to the total amount of precipitates is greater than or equal to 85%.

[0011] Further, the metallographic structure of the weathering steel is ferrite and pearlite, the ferrite grain size is 1-6 μm, and the nanoscale precipitate particle size is 1-10 nm.

[0012] In a second aspect, the embodiments of the present application provide a preparation method of the weathering steel of the first aspect, and the preparation method comprises the following steps:

[0013] obtaining a cast blank of the weathering steel;

[0014] heating and holding the cast blank;

[0015] roughly removing scales and rough rolling the heated cast blank to obtain an intermediate slab;

[0016] finely removing scales from the intermediate slab;

[0017] finely rolling the intermediate slab after the fine scale removal to obtain a strip;

[0018] laminar cooling the strip;

[0019] coiling the strip after the laminar cooling to obtain a hot-rolled steel coil;

[0020] slow cooling and holding the hot-rolled steel coil to obtain the steel for photovoltaic support.

[0021] Further, the process parameters of the heating comprise that the heating temperature is 1260-1300 ℃, and the holding time is 2.0-2.5 h; and / or

[0022] the process parameters of the rough rolling comprise that the total reduction is greater than 85%, the outlet temperature is 1090-1130 ℃, the R2 final pass reduction is greater than 45%, and the thickness of the intermediate slab is 30-38 mm; and / or

[0023] the fine rolling comprises F1-F7 passes, and the process parameters of the fine rolling comprise that the rolling reduction of the F7 pass is less than 10%, the fine rolling end temperature is 850-900 ℃, and the single pass reduction of F1 and F2 is 35%-40%; and / or

[0024] the process parameters of the coiling comprise that the coiling temperature is 580-650 ℃.

[0025] Further, the process parameters of the slow cooling and holding comprise that the holding time is 48 h, the starting temperature is greater than 500 ℃, and the ending temperature is less than 250 ℃; and / or

[0026] The laminar cooling adopts a front section cooling mode of upper 2 and lower 4.

[0027] Further, the process parameters of the fine descaling include that the descaling pressure is greater than 18 MPa.

[0028] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0029] The weathering steel provided by the embodiments of the present application has the following chemical components in mass fraction: Ni: 0.015% to 0.05%, Cu: 0.2% to 0.5%, Cr: 1.6% to 3.0%, C≤0.120%, and the rest is Fe and inevitable impurities; when applied to products such as photovoltaic supports, Cu and Cr are used in proportion to form a dense α-FeOOH oxide layer on the surface of the steel, preventing the matrix organization of the steel from being further corroded and improving the corrosion resistance of the steel; the addition of Ni can inhibit the copper embrittlement defect formed due to the addition of Cu; and the control of the C content can avoid the adverse effects of high C content on the corrosion resistance and low-temperature toughness of the steel. Therefore, the weathering steel provided by the embodiments of the present application can improve the weather resistance of the steel, and can be used in photovoltaic supports, thereby solving the technical problem of short service life of photovoltaic supports. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and serve to explain the principles of the present application together with the specification.

[0031] 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 here. Obviously, for those skilled in the art, other drawings can also be obtained based on these drawings without any creative effort.

[0032] Figure 1 The microstructure of the weathering steel provided by the embodiments of the present application.

[0033] Figure 2 The flowchart of the preparation method of the weathering steel provided by the embodiments of the present application. DETAILED DESCRIPTION

[0034] The advantages and various effects of the present application will be more clearly presented by the following specific embodiments and examples. Those skilled in the art should understand that these specific embodiments and examples are used to illustrate the present application, rather than limit the present application.

[0035] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0036] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0037] Weathering steel is made by adding a small amount of corrosion-resistant elements such as copper and nickel to ordinary carbon steel. Due to its excellent corrosion resistance, it is widely used in steel structures such as railways, vehicles, and bridges that are exposed to the atmosphere for a long time.

[0038] Photovoltaic (PV) mounting systems are structures designed for placing, installing, and fixing solar panels in a solar photovoltaic (PV) power generation system. They require high structural strength and rigidity, as well as good low-temperature toughness to withstand the effects of rain, snow, and other extreme weather conditions. Currently, the main material for domestic solar PV mounting systems is plain carbon steel, but this material suffers from low strength, thick dimensions, poor low-temperature toughness, and fatigue resistance. Existing treatment involves hot-dip galvanizing the surface of the plain carbon steel, but galvanizing is costly, time-consuming, and environmentally unfriendly, leading to a gradual decrease in its production.

[0039] The technical solution provided by the embodiments of the present invention is to solve the above-mentioned technical problems, and the general idea is as follows:

[0040] In a first aspect, embodiments of this application provide a weathering steel, the chemical composition of which, by mass fraction, is: Ni: 0.015%–0.05%, Cu: 0.2%–0.5%, Cr: 1.6%–3.0%, C ≤ 0.120%, with the remainder being Fe and unavoidable impurities.

[0041] This application provides a weathering steel with the following chemical composition by mass fraction: Ni: 0.015%–0.05%, Cu: 0.2%–0.5%, Cr: 1.6%–3.0%, C ≤ 0.120%, with the remainder being Fe and unavoidable impurities. When applied to products such as photovoltaic brackets, the proportionate use of Cu and Cr can form a dense α-FeOOH oxide rust layer on the steel surface, preventing further corrosion of the steel matrix and improving its corrosion resistance. The addition of Ni can suppress copper embrittlement defects caused by the addition of Cu. Controlling the C content can avoid the adverse effects of high C content on the steel's corrosion resistance and low-temperature toughness. Therefore, the weathering steel provided in this application can improve the weather resistance of steel and can thus be used in photovoltaic brackets, solving the technical problem of short service life of photovoltaic brackets.

[0042] As one embodiment of the present invention, the chemical composition of the weathering steel further includes, by mass fraction: Ti: 0.08% to 0.12%, N ≤ 0.0040%, C ≥ 0.055%.

[0043] In this application, Ti plays a role in steel by increasing its strength. Ti can combine with C to form Ti carbides, which precipitate out and have a significant precipitation strengthening effect. Adding Ti content above 0.08% can increase the yield strength of the material to over 700 MPa. However, Ti readily combines with N to form TiN, and the precipitation temperature is relatively high, resulting in coarse morphologies that are detrimental to ductility, toughness, and corrosion resistance. Therefore, considering all factors, controlling the Ti content to 0.08%–0.12% ensures the strengthening effect, ductility, toughness, and corrosion resistance of the steel.

[0044] For steels containing Nb and Ti, a higher N content can easily lead to crack defects and larger TiN precipitates in the slab.

[0045] Carbon (C) in steel contributes to its strength; a C content above 0.055% can achieve a yield strength exceeding 700 MPa. However, higher C content negatively impacts corrosion resistance, cold formability, low-temperature toughness, and weldability. Therefore, considering the material's strength, cold formability, weldability, and corrosion resistance, the C content in the steel of this invention is controlled between 0.055% and 0.12%.

[0046] As one embodiment of the present invention, the chemical composition of the weathering steel, by mass fraction, further includes: Nb: 0.015% to 0.050%, V: 0.01% to 0.10%, and Nb+V+Ti≤0.20%.

[0047] In this application, Nb and V combine with C in the steel to form (Nb, V) composite carbides, which precipitate out and inhibit the recovery and recrystallization of austenite during hot rolling, thereby controlling the ferrite phase grain size to within 6 μm. Simultaneously, precipitation strengthening increases the steel's strength to a yield strength of over 700 MPa. However, excessively high Nb and Ti contents significantly increase the rolling difficulty during hot rolling, and the strength increase and ductility decrease caused by precipitated carbides become significant. Therefore, considering both rolling difficulty and strengthening effect, the Nb content is controlled at 0.015%–0.050%, and the V content at 0.01%–0.10%. Controlling Nb+V+Ti ≤ 0.20% avoids excessive addition leading to excessively high precipitation temperatures, which can easily form large-sized liquid precipitates and negatively impact the steel's low-temperature toughness.

[0048] As one embodiment of the present invention, the chemical composition of the weathering steel, by mass fraction, further includes: Mn: 1.75%–2.20%, Al: 0.02%–0.05%; or

[0049] Mn: 1.75% ~ 2.20%, Al: 0.02% ~ 0.05%, Si ≤ 0.10%.

[0050] In this application, Mn is a solid solution strengthening element that contributes to increasing the strength and fatigue resistance of steel. However, excessively high Mn content can lead to severe banding, reducing transverse elongation and affecting cold formability. Therefore, considering the material's strength, toughness, weldability, and cold formability, the Mn content is designed to be between 1.75% and 2.2%.

[0051] Al acts as a deoxidizer during steelmaking, combining with nitrogen (N) in the steel to inhibit austenite grain growth and refine recrystallized grains during hot rolling. Incomplete deoxidation leads to decreased cold formability of the steel. However, excessive Al content results in too many AlN inclusions, reducing elongation and fatigue resistance. Therefore, considering deoxidation, grain size, and inclusion control, the Al content is controlled between 0.02% and 0.05%.

[0052] Si is a solid solution strengthening element, but when its content is high, it affects the surface quality, ductility, toughness and weldability of steel.

[0053] In this application, P and S are impurity elements in steel. P element is prone to causing center segregation of steel, which deteriorates the weldability and ductility of steel, and is preferably minimized. S element is prone to forming MnS inclusions with Mn element, which will reduce the weldability, formability, fatigue performance and low temperature toughness of steel, and is preferably minimized.

[0054] As one embodiment of the present invention, the metallographic structure of the weathering steel includes ferrite and pearlite, wherein the ferrite contains nanoscale precipitates, and the volume ratio of the nanoscale precipitates to the total precipitates is ≥85%.

[0055] In one embodiment of the present invention, the metallographic structure of the weathering steel is ferrite and pearlite, wherein the ferrite grain size is 1-6 μm and the nanoscale precipitates have a particle size of 1-10 nm.

[0056] Secondly, embodiments of this application provide a method for preparing the weathering steel described in the first aspect, the method comprising:

[0057] Obtain the weathering steel billet;

[0058] The billet is heated and held at that temperature;

[0059] The heated billet is subjected to rough descaling and rough rolling to obtain an intermediate slab.

[0060] The intermediate slab is subjected to fine descaling;

[0061] The intermediate billet after fine descaling is then fine-rolled to obtain strip steel.

[0062] The strip steel is subjected to laminar flow cooling;

[0063] The strip steel after laminar flow cooling is coiled to obtain a hot-rolled steel coil;

[0064] The hot-rolled steel coil is slowly cooled and kept warm to obtain steel for photovoltaic brackets.

[0065] As one embodiment of the present invention, the heating process parameters include: a heating temperature of 1260–1300°C and a holding time of 2.0–2.5 h; and / or

[0066] The roughing rolling process parameters include: a total reduction rate greater than 85%, an exit temperature of 1090–1130°C, a final reduction rate of R2 greater than 45%, and an intermediate slab thickness of 30–38 mm; and / or

[0067] The finishing mill includes passes F1 to F7, and the process parameters for the finishing mill include: a rolling reduction rate of <10% for pass F7, a finishing mill end temperature of 850–900℃, and a single-pass reduction rate of 35%–40% for passes F1 and F2; and / or

[0068] The winding process parameters include: winding temperature of 580-650℃.

[0069] In this application, A and / or B and / or C and / or D represent that the four schemes A, B, C, and D can be implemented individually or in any combination.

[0070] In this application, a low reduction rate in the final R2 pass easily leads to mixed crystal structure, reducing the steel's low-temperature toughness and fatigue performance, as well as the rolling stability during the finishing stage. Controlling the reduction rate in the final R2 pass to greater than 45% prevents the final R2 pass from entering the partial recrystallization zone during roughing. Controlling the intermediate slab thickness to 30-38 mm improves rolling stability. Meanwhile, the compression ratios of F1 and F2 are generally greater than 40%. To prevent the F1 and F2 passes from entering the partial recrystallization zone during finishing, their compression ratios are also controlled between 35-40%. Therefore, this method can control the uniformity of the steel structure, avoid cracking caused by mixed crystal structure, and improve the steel's formability, strength, and plasticity, making it suitable for manufacturing thin-gauge, high-strength products.

[0071] In this application, rough rolling can be performed by one pass of R1 rolling and five passes of R2 rolling; rough descaling includes four descaling passes, namely one pass of R1 descaling and passes 1, 3 and 5 of R2 descaling, to ensure that the surface iron oxide scale is completely removed.

[0072] In this application, the heating temperature and time of the continuously cast billet are determined based on the solid solution and precipitation of microalloying elements in the steel, the original austenite grain size, and rolling stability. When the heating temperature is below 1260℃, the coarse Ti carbonitrides precipitated during continuous casting remain as undissolved carbonitrides, affecting the amount of secondary precipitation and thus reducing strengthening. The coarse precipitates affect plasticity, toughness, and fatigue performance, and the rolling stability of thin gauges is poor. When the heating temperature exceeds 1300℃ and the holding time is longer than 2.5h, although the microalloying elements are fully dissolved, the austenite grains become abnormally coarse, resulting in coarse ferrite phases that cannot ensure the desired strength, cold formability, and fatigue performance.

[0073] In this application, a low roughing mill exit temperature easily leads to mixed crystal formation, reducing the steel's low-temperature toughness and fatigue performance, and also decreasing the rolling stability during the finishing mill stage. Conversely, an excessively high roughing mill exit temperature can cause partial recrystallization during the finishing mill stage, resulting in mixed crystal formation.

[0074] In this application, the finishing rolling temperature has a significant impact on the grain size and uniformity of the ferrite microstructure. When the finishing rolling temperature exceeds 900℃, the uniformity and grain size of the microstructure cannot be guaranteed, which easily leads to a decrease in the formability, low-temperature toughness, and fatigue performance of the strip. When the finishing rolling temperature is below 850℃, the rolling stability is poor, and the amount of strain-induced precipitation increases. The precipitates formed at this stage are prone to growth, which cannot ensure the low-temperature toughness and fatigue characteristics of the steel.

[0075] In this application, a coiling temperature that is too low affects the precipitation strengthening effect, while a coiling temperature that is too high affects the grain refinement strengthening effect.

[0076] As one embodiment of the present invention, the process parameters for the slow cooling and heat preservation include: a heat preservation time of 48 hours, a starting temperature greater than 500°C, and an ending temperature less than 250°C; and / or

[0077] The laminar flow cooling adopts a front-end cooling mode of 2 on top and 4 on the bottom.

[0078] In this application, the slow cooling and heat preservation process is mainly to leverage the self-tempering effect to increase the precipitation strengthening ratio and eliminate the imbalance of microstructure transformation stress, rolling stress, and cooling stress generated during the cooling stage, thereby improving the strip shape quality. The upper 2 and lower 4 front-stage cooling mode can quickly cool the strip to the supercooled austenite region to undergo microstructure transformation, ensuring the required ferrite grain size and obtaining uniform and fine precipitate particle size.

[0079] As one embodiment of the present invention, the process parameters for fine descaling include: descaling pressure greater than 18 MPa.

[0080] In this application, high-pressure water of 18MPa or above can be used for descaling before finishing rolling to completely remove the iron oxide scale from the surface of the steel, so as to prevent it from being pressed into the surface of the strip during finishing rolling and affecting the surface quality.

[0081] Tests have shown that the strip steel of this invention has a yield strength of over 700 MPa, a tensile strength of over 900 MPa, an elongation of over 19%, a yield strength ratio of ≤0.8, a half-size impact energy of ≥80 J at -40℃, and a corrosion rate of ≤20% relative to ordinary structural steel Q345B.

[0082] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0083] Example 1:

[0084] A weathering steel and its preparation method, characterized by the following steps:

[0085] (1) Smelting and continuous casting: Smelt steel according to the set composition and cast it into billets. The chemical composition is shown in Table 1 by mass percentage.

[0086] (2) Slab heating: The continuous casting slab is heated and held at 1300℃ for 2 hours to fully austenitize and ensure the dissolution of microalloying elements.

[0087] (3) Hot rolling: The heated continuous casting slab is subjected to rough descaling to remove the iron oxide scale on the surface of the strip. The descaled continuous casting slab is then rough rolled to obtain an intermediate slab. The rough rolling mode is 1+5, the total reduction rate of the rough rolling is 90%, the reduction rate of the last pass of R2 is 55%, and the descaling of passes 1, 3, and 5 is activated. The exit temperature of the rough rolling is 1130℃. The thickness of the intermediate slab is 30mm.

[0088] The intermediate slab is descaled, and the descaled intermediate slab is then finished rolled to obtain strip steel. The descaled pressure is 20 MPa. The single-pass reduction rate of F1 and F2 in the finishing rolling stage is 38%, and the rolling reduction rate of the last stand is 8%. The temperature of the strip steel after finishing rolling is 900℃.

[0089] (4) Laminar flow cooling: Laminar flow cooling is performed on the strip using a front-end cooling mode of 2 on top and 4 on the bottom.

[0090] (5) Coiling and slow cooling: The strip steel after laminar flow cooling is coiled and quickly transferred to the online slow cooling pit after being coiled off the line. It is kept warm for 48 hours before being taken out of the pit. The coiling temperature is 650℃; the pit entry temperature is 570℃; and the pit exit temperature is 245℃.

[0091] The relevant process parameters of this embodiment are shown in Table 2, and the test results of various mechanical properties of the obtained weathering steel are shown in Table 3.

[0092] Example 2:

[0093] A weathering steel and its preparation method, characterized by the following steps:

[0094] (1) Smelting and continuous casting: Smelt steel according to the set composition and cast it into billets. The chemical composition is shown in Table 1 by mass percentage.

[0095] (2) Slab heating: The continuously cast slab is heated and held at 1280℃ for 2.1h to fully austenitize and ensure the dissolution of microalloying elements;

[0096] (3) Hot rolling: The heated continuous casting slab is subjected to rough descaling to remove the iron oxide scale on the surface of the strip. The descaled continuous casting slab is then rough rolled to obtain an intermediate slab. The rough rolling mode is 1+5, the total reduction rate of the rough rolling is 88%, the reduction rate of the last pass of R2 is 50%, and the descaling of passes 1, 3, and 5 is activated. The exit temperature of the rough rolling is 1110℃. The thickness of the intermediate slab is 32mm.

[0097] The intermediate slab is descaled, and the descaled intermediate slab is then finished rolled to obtain strip steel. The descaled pressure is 22 MPa. The single-pass reduction rate of F1 and F2 in the finishing rolling stage is 35%, and the rolling reduction rate of the last stand is 9%. The temperature of the strip steel after finishing rolling is 890℃.

[0098] (4) Laminar flow cooling: Laminar flow cooling is performed on the strip using a front-end cooling mode of 2 on top and 4 on the bottom.

[0099] (5) Coiling and slow cooling: The strip steel after laminar flow cooling is coiled and quickly transferred to the online slow cooling pit after being coiled off the line. It is kept at the temperature for 48 hours before being taken out of the pit. The coiling temperature is 640℃; the pit entry temperature is 550℃; and the pit exit temperature is 242℃.

[0100] The relevant process parameters of this embodiment are shown in Table 2, and the test results of various mechanical properties of the obtained weathering steel are shown in Table 3.

[0101] Example 3:

[0102] A weathering steel and its preparation method, characterized by the following steps:

[0103] (1) Smelting and continuous casting: Smelt steel according to the set composition and cast it into billets. The chemical composition is shown in Table 1 by mass percentage.

[0104] (2) Slab heating: The continuously cast slab is heated and held at 1270℃ for 2.2h to fully austenitize and ensure the dissolution of microalloying elements;

[0105] (3) Hot rolling: The heated continuous casting slab is subjected to rough descaling to remove the iron oxide scale on the surface of the strip. The descaled continuous casting slab is then rough rolled to obtain an intermediate slab. The rough rolling mode is 1+5, the total reduction rate of the rough rolling is 86%, the reduction rate of the last pass of R2 is 47%, and the descaling of passes 1, 3, and 5 is activated. The exit temperature of the rough rolling is 1090℃. The thickness of the intermediate slab is 34mm.

[0106] The intermediate slab is descaled, and the descaled intermediate slab is then finished rolled to obtain strip steel. The descaled pressure is 25 MPa. The single-pass reduction rate of F1 and F2 in the finishing rolling stage is 40%, and the rolling reduction rate of the last stand is 7%. The temperature of the strip steel after finishing rolling is 880℃.

[0107] (4) Laminar flow cooling: Laminar flow cooling is performed on the strip using a front-end cooling mode of 2 on top and 4 on the bottom.

[0108] (5) Coiling and slow cooling: The strip steel after laminar flow cooling is coiled and quickly transferred to the online slow cooling pit after being coiled off the line. It is kept warm for 48 hours before being taken out of the pit. The coiling temperature is 630℃; the pit entry temperature is 540℃; and the pit exit temperature is 240℃.

[0109] The relevant process parameters of this embodiment are shown in Table 2, and the test results of various mechanical properties of the obtained weathering steel are shown in Table 3.

[0110] Example 4:

[0111] A weathering steel and its preparation method, characterized by the following steps:

[0112] (1) Smelting and continuous casting: Smelt steel according to the set composition and cast it into billets. The chemical composition is shown in Table 1 by mass percentage.

[0113] (2) Slab heating: The continuously cast slab is heated and held at 1265℃ for 2.5h to fully austenitize and ensure the dissolution of microalloying elements;

[0114] (3) Hot rolling: The heated continuous casting slab is subjected to rough descaling to remove the iron oxide scale on the surface of the strip. The descaled continuous casting slab is then rough rolled to obtain an intermediate slab. The rough rolling mode is 1+5, the total reduction rate of the rough rolling is 89%, the reduction rate of the last pass of R2 is 50%, and the descaling of passes 1, 3, and 5 is activated. The exit temperature of the rough rolling is 1100℃. The thickness of the intermediate slab is 34mm.

[0115] The intermediate slab is descaled, and the descaled intermediate slab is then finished rolled to obtain strip steel. The descaled pressure is 23 MPa. The single-pass reduction rate of F1 and F2 in the finishing rolling stage is 38%, and the rolling reduction rate of the last stand is 8%. The temperature of the strip steel after finishing rolling is 860℃.

[0116] (4) Laminar flow cooling: Laminar flow cooling is performed on the strip using a front-end cooling mode of 2 on top and 4 on the bottom.

[0117] (5) Coiling and slow cooling: The strip steel after laminar flow cooling is coiled and quickly transferred to the online slow cooling pit after being coiled off the line. It is kept warm for 48 hours before being taken out of the pit. The coiling temperature is 610℃; the pit entry temperature is 520℃; and the pit exit temperature is 220℃.

[0118] The relevant process parameters of this embodiment are shown in Table 2, and the test results of various mechanical properties of the obtained weathering steel are shown in Table 3.

[0119] Example 5:

[0120] A weathering steel and its preparation method, characterized by the following steps:

[0121] (1) Smelting and continuous casting: Smelt steel according to the set composition and cast it into billets. The chemical composition is shown in Table 1 by mass percentage.

[0122] (2) Slab heating: The continuously cast slab is heated and held at 1265℃ for 2.5h to fully austenitize and ensure the dissolution of microalloying elements;

[0123] (3) Hot rolling: The heated continuous casting slab is subjected to rough descaling to remove the iron oxide scale on the surface of the strip. The descaled continuous casting slab is then rough rolled to obtain an intermediate slab. The rough rolling mode is 1+5, the total reduction rate of the rough rolling is 89%, the reduction rate of the last pass of R2 is 50%, and the descaling of passes 1, 3, and 5 is activated. The exit temperature of the rough rolling is 1105℃. The thickness of the intermediate slab is 34mm.

[0124] The intermediate slab is descaled, and the descaled intermediate slab is then finished rolled to obtain strip steel. The descaled pressure is 23 MPa. The single-pass reduction rate of F1 and F2 in the finishing rolling stage is 38%, and the rolling reduction rate of the last stand is 8%. The temperature of the strip steel after finishing rolling is 850℃.

[0125] (4) Laminar flow cooling: Laminar flow cooling is performed on the strip using a front-end cooling mode of 2 on top and 4 on the bottom.

[0126] (5) Coiling and slow cooling: The strip steel after laminar flow cooling is coiled and quickly transferred to the online slow cooling pit after being coiled off the line. It is kept warm for 48 hours before being taken out of the pit. The coiling temperature is 605℃; the pit entry temperature is 515℃; and the pit exit temperature is 215℃.

[0127] The relevant process parameters of this embodiment are shown in Table 2, and the test results of various mechanical properties of the obtained weathering steel are shown in Table 3.

[0128] Comparative Example 1:

[0129] The chemical composition ratio of the steel was changed (as shown in Table 1), the slow cooling pit operation in Example 1 was cancelled, and the process parameters in Example 1 were adjusted. The adjusted process parameters are shown in Table 2. The remaining operations are the same as in Example 1.

[0130] Comparative Example 2:

[0131] The chemical composition ratio of the steel was changed (as shown in Table 1), the slow cooling pit operation in Example 1 was cancelled, and the process parameters in Example 1 were adjusted. The adjusted process parameters are shown in Table 2. The remaining operations are the same as in Example 1.

[0132] Comparative Example 3:

[0133] The chemical composition ratio of the steel was changed (as shown in Table 1), the slow cooling pit operation in Example 1 was cancelled, and the process parameters in Example 1 were adjusted. The adjusted process parameters are shown in Table 2. The remaining operations are the same as in Example 1.

[0134] Table 1. Chemical composition of steel (wt.%, balance: Fe and other unavoidable impurities)

[0135]

[0136] Table 2 Process Parameters

[0137]

[0138] Table 3. Test results of various mechanical properties of weathering steel

[0139]

[0140]

[0141] As shown in Table 3, the weathering steel of this invention has a yield strength greater than 700 MPa, reaching a maximum of 762 MPa; a tensile strength greater than 900 MPa, reaching a maximum of 964 MPa; and an elongation at break greater than or equal to 19.0%, reaching a maximum of 21.0%. Furthermore, it passes the 180°d=1a cold bending test; the impact energy at -40℃ half-size is ≥80 J; and its corrosion rate is ≤20% compared to ordinary structural steel Q345B. Therefore, the photovoltaic bracket steel using this weathering steel strip possesses excellent cold forming performance, weldability, and corrosion resistance.

[0142] Examples 1-5 all exhibit a ferrite microstructure with an average grain size of 1-6 μm and an average Ti carbonitride particle size between 1-10 nm, with nanoscale precipitates comprising ≥85%. The strip surface is free of edge peeling and red iron oxide scale, and the iron oxide scale does not detach during the forming process.

[0143] As can be seen from Comparative Examples 1-3, Comparative Example 1 has a similar chemical composition to Comparative Example 1. Due to its different rolling process, especially the high coiling temperature of 680℃, although it has excellent corrosion resistance, its strength is low, with yield strength and tensile strength below 700MPa and 900MPa, respectively, and its yield strength ratio is higher than 0.8. Comparative Example 2 did not add microalloying corrosion-resistant elements such as Cu, Cr, and Ni. Although its yield strength reached 700MPa, its tensile strength was only 790MPa, failing to reach 900MPa, and its yield strength ratio was as high as 0.9. At the same time, its corrosion resistance index was 90%, indicating a lack of corrosion resistance. Comparative Example 3 is a commonly used photovoltaic bracket steel, which adopts a medium-carbon microalloying composition system. Due to insufficient addition of strengthening elements such as Nb, Ti, and Cr, although its elongation at break is as high as 26%, its yield strength and tensile strength are 470 and 600MPa, respectively, indicating insufficient strength. At the same time, its low-temperature toughness does not meet 45J, and its atmospheric corrosion resistance is also poor.

[0144] In summary, this application, based on low carbon, low silicon, and low manganese, incorporates a reasonable ratio of weather-resistant elements such as copper, chromium, and nickel, combined with a hot rolling process involving high-temperature extrusion, high-temperature final rolling, and high-temperature coiling, to obtain hot-rolled strip steel with excellent cold formability, weldability, low-temperature toughness, fatigue performance, and weather resistance. This ensures that the processing and use of photovoltaic bracket steel meets the requirements for strength, low-temperature toughness, fatigue performance, corrosion resistance, structural stability, long service life, and environmental friendliness. Through product composition and process design, this product can solve the problems of poor rolling stability of thin-gauge steel, large fluctuations in the mechanical properties of high-Ti steel, and the shortcomings of existing steel brackets such as low strength, thick gauge, poor low-temperature toughness and fatigue, high galvanizing cost and environmental unfriendliness. It achieves a strip steel yield strength of over 700MPa, tensile strength of over 900MPa, elongation of over 19%, yield strength ratio ≤0.8, half-size impact energy at -40℃ ≥80J, and corrosion rate ≤20% compared to ordinary structural steel Q345B. It is suitable for the processing and performance requirements of photovoltaic bracket steel. The production process of this product is short, easy to operate, and environmentally friendly.

[0145] It should be understood that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0146] It should be noted that in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Additionally, the term "and / or" as used herein is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone.

[0147] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A weathering steel, characterized in that, The chemical composition of the weathering steel, by mass fraction, is as follows: Ni: 0.015%–0.05%, Cu: 0.2%–0.5%, Cr: 1.6%–3.0%, 0.055% ≤ C ≤ 0.120%, Ti: 0.08%–0.12%, N ≤ 0.0040%, Nb: 0.015%–0.050%, V: 0.01%–0.10%, and Nb+V+Ti ≤ 0.20%, Mn: 1.75%–2.20%, Al: 0.02%–0.05%, Si ≤ 0.10%, and the remainder... The weathering steel contains Fe and unavoidable impurities; its microstructure includes ferrite and pearlite, the ferrite contains nanoscale precipitates, the nanoscale precipitates account for ≥85% of the total volume of precipitates, the ferrite grain size is 1-6 μm, the nanoscale precipitates have a particle size of 1-10 nm, the weathering steel has a yield strength ≥700 MPa, tensile strength ≥900 MPa, elongation ≥19%, yield strength ratio ≤0.8, and half-size impact energy at -40℃ ≥80 J; the preparation method of the weathering steel includes heating and holding the cast billet at a certain temperature. The heated slab is subjected to rough descaling and rough rolling to obtain an intermediate slab; the intermediate slab is subjected to fine descaling; the finely descaled intermediate slab is finely rolled to obtain a strip; the strip is subjected to laminar flow cooling; the laminar flow cooled strip is coiled to obtain a hot-rolled steel coil; the hot-rolled steel coil is slowly cooled and held at the same temperature to obtain weathering steel. The heating temperature is 1260–1300℃, and the holding time is 2.0–2.5 h. The roughing rolling process parameters include: a total reduction rate greater than 85%, an exit temperature of 1090–1130℃, a reduction rate of greater than 45% in the final pass of R2, and a thickness of 30–38 mm for the intermediate slab. The finishing rolling includes passes F1–F7, and the finishing rolling process parameters include: a rolling reduction rate of <10% in pass F7, a finishing rolling end temperature of 850–900℃, and a single-pass reduction rate of 35%–40% for passes F1 and F2. The coiling temperature is 580–650℃. The slow cooling and holding process parameters include: a holding time of 48 h, a starting temperature greater than 500℃, and an ending temperature less than 250℃. The laminar flow cooling adopts a front-stage cooling mode of 2 at the top and 4 at the bottom.

2. A method for preparing weathering steel according to claim 1, characterized in that, The preparation method includes: Obtain the weathering steel billet; The billet is heated and held at that temperature; The heated billet is subjected to rough descaling and rough rolling to obtain an intermediate slab; The intermediate slab is then subjected to fine descaling; The intermediate billet after fine descaling is then precision rolled to obtain strip steel. The strip steel is subjected to laminar flow cooling; The strip steel after laminar flow cooling is coiled to obtain a hot-rolled steel coil; The hot-rolled steel coil is slowly cooled and kept at a constant temperature to obtain weather-resistant steel.

3. The preparation method according to claim 2, characterized in that, The process parameters for fine descaling include: descaling pressure greater than 18 MPa.

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