Weathering steel sheet and method for manufacturing the same

Abstract

This application relates to a weathering steel plate and its preparation method. The weathering steel plate comprises: C: 0.07-0.11%, Si: 0.2-0.6%, Mn: 0.3-0.5%, Cu: 0.2-0.4%, Ni: 0.01-0.03%, Ti: 0.01-0.02%, Zr: 0-0.01%, Cr: 0.20-0.40%, P: 0.06-0.12%, N: 0.002 -0.004%; The preparation method involves continuous casting, roller cooling, heating, and rolling of molten steel; the addition of zirconium can improve the comprehensive performance of steel by fixing nitrogen, refining grains, and stabilizing rust layer; before heating the continuously cast billet, the furnace temperature of the surface layer of the continuously cast billet is controlled at 550-600℃, which can inhibit the precipitation of AlN grain boundaries on the surface layer of the continuously cast billet, while refining the surface grains and improving the grain boundary bonding force; thus solving the defects of edge point-line peeling and red rust.

Description

Technical Field

[0001] This application relates to the field of steel preparation technology, and in particular to a weathering steel plate and its preparation method. Background Technology

[0002] Weathering steel is a type of steel made by adding alloying elements (such as copper, chromium, nickel, and phosphorus) through a specific process. Its core advantage lies in its ability to form a dense oxide layer (rust layer) when exposed to the natural environment, thereby delaying corrosion. Hot-rolled weathering steel, with its characteristics of being paint-free, having a long service life, and requiring low maintenance, is widely used in bridges and building structures, railway vehicles and containers, transmission towers and power facilities, and landscape and art installations. However, different degrees of edge defects occur during the production of hot-rolled weathering steel of varying thicknesses. Specifications with a thickness of 4mm or more exhibit less severe edge defects, mainly point-like peeling defects, while specifications with a thickness less than 4mm show more severe edge defects, primarily linear peeling defects, along with a small amount of red rust defects. This undoubtedly affects the surface coating quality of the end-user's product. Currently, most research on the quality problems of weathering steel focuses on waviness and copper embrittlement defects, but research on improving the edge surface quality of weathering steel is still limited.

[0003] In view of this, it is necessary to design a weathering steel plate and its preparation method to solve the above problems. Summary of the Invention

[0004] This application provides a weathering steel plate and its preparation method to solve the problem of edge defects in current weathering steel.

[0005] In a first aspect, this application provides a weathering steel plate, wherein the chemical composition of the weathering steel plate, by mass percentage, comprises: C: 0.07%-0.11%, Si: 0.2%-0.6%, Mn: 0.3%-0.5%, Cu: 0.20%-0.40%, Ni: 0.01%-0.03%, Ti: 0.01%-0.02%, Zr: 0-0.01%, Cr: 0.20%-0.40%, P: 0.06%-0.12%, N: 0.002%-0.004%, with the remainder being Fe and unavoidable impurities; wherein the total content of Ti and Zr is 0.01%-0.03%.

[0006] In some embodiments, the microstructure of the weathering steel plate includes ferrite and pearlite; by volume percentage, the ferrite accounts for 80%-95% and the pearlite accounts for 5%-20% in the weathering steel plate; the grain size of both the ferrite and the pearlite is 5μm-10μm.

[0007] Secondly, this application provides a method for preparing the above-mentioned weathering steel plate, comprising the following steps: Molten steel is provided, and the molten steel is smelted and continuously cast to obtain a continuously cast billet; The continuous casting billet is subjected to roller cooling treatment to obtain a pre-cooled continuous casting billet; the surface temperature of the pre-cooled continuous casting billet is 550℃-600℃. The pre-cooled continuous casting billet is heated to obtain a hot casting billet; The hot-cast billet is rolled to obtain a hot-rolled plate; The hot-rolled plate is cooled to obtain the weathering steel plate.

[0008] In some embodiments, the roller cooling process includes: spraying water onto the surface of the continuously cast billet located on the roller table using a nozzle for 2-5 minutes; the water flow velocity from the nozzle is 5-10 m / s.

[0009] In some embodiments, the heat treatment includes: heating the pre-cooled continuous casting billet to 1160℃-1190℃ and holding it at 1160℃-1190℃ for 160min-200min.

[0010] In some embodiments, if the thickness of the hot-rolled plate is <4.0 mm, the pre-cooled continuous casting billet is heated to 1170℃-1190℃ and held at 1170℃-1190℃ for 180 min-200 min during the heat treatment; if the thickness of the hot-rolled plate is ≥4.0 mm, the pre-cooled continuous casting billet is heated to 1160℃-1180℃ and held at 1160℃-1180℃ for 160 min-180 min during the heat treatment.

[0011] In some embodiments, the furnace atmosphere during the heating treatment is a weakly reducing atmosphere; the excess air coefficient in the furnace is 0.95-1.0.

[0012] In some embodiments, the rolling process includes sequentially performing rough rolling and finish rolling on the hot-cast billet; the rolling mill used in the rough rolling process includes a first rolling mill and a second rolling mill; when using the first rolling mill, the hot-cast billet is rolled three times; when using the second rolling mill, the hot-cast billet that has undergone the three rolling processes is rolled five times.

[0013] In some embodiments, if the thickness of the hot-rolled plate is <4.0mm, the width reduction of the vertical roll of the vertical roll side press must be ≤60mm during the rough rolling process; if the thickness of the hot-rolled plate is ≥4.0mm, the width reduction of the vertical roll of the vertical roll side press must be ≤100mm during the heating process.

[0014] In some embodiments, the exit temperature of the roughing process is 1050℃-1100℃.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: 1. The weathering steel plate provided in this application embodiment comprises: C: 0.07%-0.11%, Si: 0.2%-0.6%, Mn: 0.3%-0.5%, Cu: 0.20%-0.40%, Ni: 0.01%-0.03%, Ti: 0.01%-0.02%, Zr: 0-0.01%, Cr: 0.20%-0.40%, P: 0.06%-0.12%, N: 0.002%-0.004%, with the remainder being Fe and unavoidable... Impurities; the total content of Ti and Zr is 0.01%-0.03%; this reduces the occurrence of edge-shaped peeling defects and red rust defects in the subsequently produced steel; the addition of trace amounts of titanium and zirconium can fix nitrogen, change the morphology of inclusions in the steel, and reduce the harm of low-melting-point AlN grain boundary precipitation; in particular, Zr in weathering steel can significantly improve the comprehensive performance of the steel through a triple mechanism of fixing nitrogen, refining grains, and stabilizing the rust layer, and the prepared steel is fully suitable for resisting Cl - Scenarios with stringent requirements for corrosion resistance and weldability.

[0016] 2. The method for preparing the weathering steel plate provided in this application embodiment involves continuously casting the target molten steel to obtain a continuously cast billet, and then sequentially subjecting the billet to roller cooling, heating, rolling, and cooling treatments to finally obtain the weathering steel plate. This method can solve the edge-shaped peeling defects and red rust defects. Specifically, the roller cooling process performed before heating the continuously cast billet controls the furnace entry temperature of the billet surface layer at 550℃-600℃, which can suppress AlN grain boundary precipitation on the billet surface layer, refine the surface grains, and improve grain boundary bonding. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A morphological diagram of a weathering steel plate provided in Embodiment 1 of this application is shown; Figure 2 A morphological diagram of a weathering steel plate provided in Comparative Example 1 of this application is shown; Figure 3 A morphological diagram of a weathering steel plate provided in Comparative Example 2 of this application is shown; Figure 4 A morphological diagram of a weathering steel plate provided in Comparative Example 3 of this application is shown; Figure 5 A morphological diagram of a weathering steel plate provided in Comparative Example 4 of this application is shown. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] Various embodiments of this application may exist in the form of a range. It should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application. Therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that 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., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in this application, it means including any referenced number (fraction or integer) within the indicated range. Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this application can be purchased commercially or prepared by existing methods. In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. In addition, in this application, the terms "comprising," "including," etc., mean "including but not limited to." In this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any actual relationship or order between these entities or operations. In this application, "and / or" describes 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. A and B can be singular or plural. In this application, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or multiple.

[0022] This application provides a weathering steel plate, the chemical composition of which, by mass percentage, comprises: C: 0.07%-0.11%, Si: 0.2%-0.6%, Mn: 0.3%-0.5%, Cu: 0.20%-0.40%, Ni: 0.01%-0.03%, Ti: 0.01%-0.02%, Zr: 0-0.01%, Cr: 0.20%-0.40%, P: 0.06%-0.12%, N: 0.002%-0.004%, with the remainder being Fe and unavoidable impurities; wherein the total content of Ti and Zr is 0.01%-0.03%.

[0023] This reduces the occurrence of edge-shaped peeling defects and red rust defects in the steel produced subsequently.

[0024] The design principles of each chemical element in this application are as follows: Carbon (C): Carbon is a core element for solid solution strengthening and carbide formation (such as Fe3C), directly affecting the strength and hardness of steel. Low-carbon design significantly reduces cold brittleness and aging sensitivity, and optimizes weldability. However, excessively high carbon content (>0.12%) easily forms coarse carbides, destroying the density of the rust layer and accelerating localized corrosion of the steel. Therefore, considering the overall material properties, the C content in the weathering steel of this application is controlled at 0.07%-0.11%; preferably, the C content is 0.08%-0.10%.

[0025] Silicon (Si): Silicon is dissolved in ferrite, which can improve the strength of steel, but also slightly reduces its plasticity. In addition, silicon acts as a strong deoxidizer, reducing the formation of oxide inclusions in steel and improving the purity of molten steel. Furthermore, silicon can promote the formation of amorphous FeOOH in the rust layer, inhibiting the penetration of corrosive media and enhancing the corrosion resistance of steel. However, excessive silicon content can easily lead to red rust defects on the surface of the steel plate. Therefore, considering all factors, the silicon content in the weathering steel of this application is controlled at 0.2%-0.6%; preferably, the Si content is 0.3%-0.45%.

[0026] Manganese (Mn): Manganese improves the strength of steel through solid solution strengthening, but if the manganese content is greater than 0.5%, it will lead to a decrease in the plasticity of the steel. Therefore, taking all factors into consideration, this application controls the Mn content at 0.3%-0.5%; preferably, the Mn content is 0.35%-0.45%.

[0027] Copper (Cu): Cu accumulates in rust layers and can catalyze the formation of a dense α-FeOOH protective layer, significantly improving the weather resistance of steel; however, excessive Cu content (>0.4%) can easily cause hot brittleness in steel. Therefore, considering all factors, this application controls the Cu content to 0.20%-0.40%; preferably, the Cu content is 0.25%-0.35%.

[0028] Phosphorus (P): The simultaneous addition of Cu and P can synergistically promote the growth of a dense rust layer in steel, further improving the weather resistance of the steel; however, excessive P can lead to grain boundary embrittlement. Therefore, taking all factors into consideration, this application controls the P content at 0.06%-0.12%, preferably 0.08%-0.10%.

[0029] Nickel (Ni): Adding a small amount of nickel can improve the low-temperature plasticity and impact resistance of steel, while suppressing hot working cracks caused by Cu enrichment; however, excessive Ni will form NiO enrichment on the steel surface, and the oxides are easily pressed into the matrix, causing surface scabs. Therefore, taking all factors into consideration, this application controls the Ni content at 0.01%-0.03%; preferably, the Ni content is 0.015%-0.025%.

[0030] Adding trace amounts of titanium (Ti) and zirconium (Zr) can fix nitrogen, alter the morphology of inclusions in steel, and reduce the harmful effects of low-melting-point AlN grain boundary precipitation. In particular, Zr in weathering steel significantly improves the overall performance of the steel through a triple mechanism of nitrogen fixation, grain refinement, and rust layer stabilization (improving the plasticity of the slab edge). Furthermore, the resulting steel is perfectly suited for resisting Cl-. - In applications with stringent requirements for corrosion resistance and weldability (such as cross-sea bridges and coastal buildings), this application controls the total content of Ti and Zr to 0.01%-0.03%; preferably, the total content of Ti and Zr is 0.015%-0.025%.

[0031] Chromium (Cr): Chromium improves hardenability and enhances corrosion resistance through solid solution strengthening. Appropriate amounts of chromium can stabilize austenite, but excessive amounts will reduce plasticity and weldability. Therefore, considering all factors, the Cr content in this application is controlled at 0.20%-0.40%.

[0032] As an optional implementation, in this embodiment of the application, the microstructure of the weathering steel plate includes ferrite and pearlite; by volume percentage, the ferrite accounts for 80%-95% and the pearlite accounts for 5%-20% in the weathering steel plate; the grain size of both the ferrite and the pearlite is 5μm-10μm.

[0033] Based on a general inventive concept, this application provides a method for preparing the above-mentioned weathering steel plate, comprising the following steps: Step S1: Provide molten steel, smelt and continuously cast the molten steel to obtain a continuously cast billet; Step S2: The continuous casting billet is subjected to roller cooling treatment to obtain a pre-cooled continuous casting billet; the surface temperature of the pre-cooled continuous casting billet is 550℃-600℃. Step S3: Heat the pre-cooled continuous casting billet to obtain a hot casting billet; Step S4: Roll the hot-cast billet to obtain a hot-rolled plate; Step S5: Cool the hot-rolled plate to obtain the weathering steel plate.

[0034] The method for preparing weathering steel plates provided in this application involves continuously casting qualified target molten steel to obtain a continuously cast billet, and then sequentially subjecting the billet to roller cooling, heating, rolling, and cooling treatments to finally obtain a weathering steel plate; this can solve the defects of edge point-line peeling and red rust.

[0035] The furnace entry condition and heating process of the continuously cast billet have a significant impact on its surface quality after exiting the furnace. After the billet is produced, the temperature drops rapidly at the edges, making them prone to being within the austenite transformation temperature range before entering the furnace, resulting in uneven surface microstructure. Furthermore, during the phase transformation process, AlN and other particles precipitate at grain boundaries, and the resulting structural and phase transformation stresses weaken the grain boundaries, leading to microcracks in the slab. Therefore, before heating the continuously cast billet, a roller cooling process is used to control the furnace entry temperature of the billet surface below 700℃, preferably 550℃-600℃. This can suppress AlN grain boundary precipitation on the billet surface, refine the surface grains, and improve grain boundary bonding.

[0036] As an optional implementation, in this embodiment of the application, the roller cooling process includes: spraying water onto the surface of the continuously cast billet located on the roller table for 2-5 minutes using a nozzle; the water flow velocity from the nozzle is 5-10 m / s.

[0037] Thus, the surface temperature of the billet drops below the two-phase temperature, because the two-phase temperature of 650℃-800℃ is the brittle temperature range of the billet. In this temperature range, even small mechanical stresses (such as the pressure of the straightening rollers, roller friction, and stress caused by misalignment of the support rollers) are enough to cause cracks on the surface or under the surface of the billet.

[0038] As an optional implementation, in this embodiment of the application, the heat treatment includes: heating the pre-cooled continuous casting billet to 1160℃-1190℃, and holding it at 1160℃-1190℃ for 160min-200min.

[0039] In some embodiments of this application, when a heating furnace is used to heat the pre-cooled continuously cast billet, if the heating temperature and holding time are not properly controlled, alloying elements such as Cu and P are prone to enrichment at the grain boundaries. This phenomenon can lead to mixed grain problems, resulting in a significant decrease in grain boundary bonding. During subsequent roughing and vertical roll widening processes, this defect exacerbates surface grain boundary cracking, ultimately leading to peeling defects. After peeling defects form, oxides of elements such as Si and Cr will form in the defect area. This not only makes the deformation behavior of the peeling area more complex but also increases the probability of iron oxide scale breakage, ultimately leading to severe red rust defects. Therefore, properly controlling the heating temperature of the billet, the time spent in the furnace, and the oxidizing atmosphere within the heating furnace are crucial to avoiding the aforementioned defects.

[0040] As an optional implementation, in this embodiment of the application, if the thickness of the hot-rolled plate is <4.0mm, the pre-cooled continuous casting billet is heated to 1170℃-1190℃ and held at 1170℃-1190℃ for 180min-200min during the heat treatment; if the thickness of the hot-rolled plate is ≥4.0mm, the pre-cooled continuous casting billet is heated to 1160℃-1180℃ and held at 1160℃-1180℃ for 160min-180min during the heat treatment.

[0041] Experiments revealed that, in order to further reduce the occurrence of edge defects in steel, different heating temperatures and holding times were used for hot-rolled plates of different thicknesses.

[0042] As an optional implementation, in this embodiment of the application, the heating furnace atmosphere during the heating treatment is a weakly reducing atmosphere; the excess air coefficient in the heating furnace is 0.95-1.0.

[0043] This can reduce the oxidation rate of continuously cast billets and the probability of red rust forming on their edges.

[0044] As an optional implementation, in this embodiment of the application, the rolling process includes sequentially performing rough rolling and finish rolling on the hot-cast billet; the rolling mill used in the rough rolling process includes: a first rolling mill and a second rolling mill; when using the first rolling mill, the hot-cast billet is rolled three times; when using the second rolling mill, the hot-cast billet that has undergone the three rolling processes is rolled five times.

[0045] The generation of edge defects is concentrated in the roughing rolling stage, which includes two rolling mills, R1 and R2. Practice shows that even if the composition control of the continuously cast billet and the heating furnace process are in good condition, an inappropriate rolling mode can still affect the surface layer of the slab to some extent. In existing technologies, the roughing rolling process uses a "1+5" rolling mode. This mode suffers from excessively high reduction rates in single-pass rolling—excessive reduction rates can easily cause the slab surface to crack due to excessive rolling stress, ultimately leading to surface defects. To address this issue, this application optimizes the roughing rolling process by adopting a "3+5" rolling mode. By rationally allocating the reduction amount in each pass, the rolling load can be effectively reduced, thus creating favorable conditions for mitigating surface defects.

[0046] As an optional implementation, in this embodiment, the slab widens during the rolling process, thus requiring the use of R1 and R2 vertical rolls to reduce its width at the edges. During this process, the deformation behavior of the slab edges is relatively complex. To address this characteristic, the width reduction amount of the vertical rolls needs to be differentiated based on the thickness of the hot-rolled plate: for hot-rolled plates with a thickness < 4.0 mm, the width reduction amount should be ≤ 60 mm; for hot-rolled plates with a thickness ≥ 4.0 mm, the width reduction amount should be ≤ 100 mm. This control method avoids micro-cracks at the slab edges due to excessive deformation, thereby preventing the occurrence of peeling and red rust defects.

[0047] As an optional implementation, in this embodiment of the application, the exit temperature of the roughing process is 1050℃-1100℃.

[0048] The present application is further illustrated below with reference to specific embodiments. 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.

[0049] Examples 1-7 Examples 1-7 each provide a method for preparing weathering steel plates, comprising the following steps: Step S1: Provide molten steel, smelt and continuously cast the molten steel to obtain a continuously cast billet at a temperature of 800℃-900℃; Step S2: Perform roller cooling treatment on the continuous casting billet to obtain a pre-cooled continuous casting billet; the surface temperature of the pre-cooled continuous casting billet is 550℃-600℃; the roller cooling treatment includes: using a nozzle to cool the surface of the continuous casting billet located on the roller for 2min-5min; the water flow velocity of the nozzle is 5m / s-10m / s. Step S3: Heat the pre-cooled continuous casting billet to obtain a hot casting billet; the heat treatment includes: heating the pre-cooled continuous casting billet to 1160℃-1190℃ and holding it at 1160℃-1190℃ for 160min-200min; the heating furnace atmosphere during the heat treatment is a weakly reducing atmosphere, and the excess air coefficient in the heating furnace is 0.95-1.0; Step S4: Roll the hot-cast billet to obtain a hot-rolled plate; Specifically, if the thickness of the hot-rolled plate is <4.0mm, the pre-cooled continuous casting billet shall be heated to 1170℃-1190℃ and held at 1170℃-1190℃ for 180min-200min before heat treatment; if the thickness of the hot-rolled plate is ≥4.0mm, the pre-cooled continuous casting billet shall be heated to 1160℃-1180℃ and held at 1160℃-1180℃ for 160min-180min before heat treatment. The rolling process includes sequential roughing and finishing of the hot-cast billet; the rolling mills used in the roughing process include: a first rolling mill and a second rolling mill; when using the first rolling mill, the hot-cast billet is rolled three times; when using the second rolling mill, the hot-cast billet that has been rolled three times is rolled five times. If the required thickness of the hot-rolled plate is <4.0mm, the reduction in the width of the vertical rolls of the vertical roll side press should be ≤60mm during rough rolling; if the required thickness of the hot-rolled plate is ≥4.0mm, the reduction in the width of the vertical rolls of the vertical roll side press should be ≤100mm during heat treatment. The exit temperature of the rough rolling process is 1050℃-1100℃; Step S5: Cool the hot-rolled plate to obtain weathering steel plate.

[0050] The chemical composition of the prepared weathering steel plate, by mass percentage, includes: C: 0.07%-0.11%, Si: 0.2%-0.6%, Mn: 0.3%-0.5%, Cu: 0.20%-0.40%, Ni: 0.01%-0.03%, Ti: 0.01%-0.02%, Zr: 0-0.01%, Cr: 0.20%-0.40%, P: 0.06%-0.12%, N: 0.002%-0.004%, with the remainder being Fe and unavoidable impurities; among which, the total content of Ti and Zr is 0.01%-0.03%.

[0051] The chemical element content of the weathering steel plates prepared in Examples 1-7 is shown in Table 1 (the remainder is Fe and unavoidable impurities). The specific parameters of each process in Examples 1-7 are shown in Table 2.

[0052] Comparative Examples 1-9 Comparative Examples 1 to 9 each provide a method for preparing weathering steel plates. The specific process parameters and the chemical element content in the weathering steel plates are shown in Tables 1 and 2.

[0053] Note: Differences in ingredients: The difference between Example 2 and Comparative Examples 5-6 and Example 1 is that the contents of Cu and Zr are different; the other steps and contents are the same as in Example 1, and will not be repeated here.

[0054] The difference between Example 3 and Comparative Examples 7-8 and Example 1 is that the contents of Ti and Zr are different; the other steps and contents are the same as those in Example 1, and will not be repeated here.

[0055] Differences in process: The difference between Example 4 and Comparative Examples 5-6 and Example 1 is that the surface temperature of the pre-cooled continuous casting billet is different; the other steps and contents are the same as those in Example 1, and will not be repeated here.

[0056] The difference between Example 5 and Comparative Examples 7-8 and Example 1 is that the heat treatment time is different; the other steps and contents are the same as in Example 1, and will not be repeated here.

[0057] The difference between Example 6 and Comparative Example 9 and Example 1 is the amount of width reduction of the vertical roller; the remaining steps and contents are the same as in Example 1, and will not be repeated here.

[0058] The difference between Example 7 and Example 1 is that the reduction in the width of the vertical roll and the thickness of the hot-rolled plate are different. The remaining steps and contents are the same as those in Example 1, and will not be repeated here.

[0059] Table 1. Mass percentage (%) of each chemical element in the weathering steel plates prepared in Examples 1-3

[0060] Table 2 Specific parameters of each process in Examples 1-3

[0061] The results showed that the edge-shaped peeling defects and edge red rust defects of the weathering steel plates prepared in the examples were reduced, and the control effect was successful. However, the weathering steel plates prepared in the comparative examples still showed a certain degree of defects.

[0062] Furthermore, electron microscopy was performed on the steel plates prepared in Examples 1-4 and Example 1, and the results are as follows: Figures 1-5 As shown, the results indicate that the surface of the weathering steel plate in Example 1 has no obvious defects.

[0063] In summary, this invention provides a weathering steel plate and its preparation method. The weathering steel plate comprises: C: 0.07%-0.11%, Si: 0.2%-0.6%, Mn: 0.3%-0.5%, Cu: 0.20%-0.40%, Ni: 0.01%-0.03%, Ti: 0.01%-0.02%, Zr: 0-0.01%, Cr: 0.20%-0.40%, P: 0.06%-0.12%, N: 0.002%-0.004%, with the remainder being Fe. And unavoidable impurities; among which, the total content of Ti and Zr is 0.01%-0.03%; which makes the steel produced later less prone to edge-shaped peeling defects and red rust defects; among which, the addition of trace amounts of titanium and zirconium can fix nitrogen, change the morphology of inclusions in steel, and reduce the harm of low-melting-point AlN grain boundary precipitation; in particular, Zr in weathering steel can significantly improve the comprehensive performance of steel through a triple mechanism of fixing nitrogen, refining grains, and stabilizing rust layer, and the prepared steel is fully suitable for resisting Cl -This method is suitable for applications with stringent requirements regarding corrosion resistance and weldability. It involves continuously casting the target molten steel to obtain a continuously cast billet, which is then subjected to a series of processes including roller cooling, heating, rolling, and cooling to ultimately obtain a weathering steel plate. This process effectively addresses edge defects such as linear peeling and red rust. Specifically, the roller cooling process before heating the billet controls the furnace entry temperature of the billet surface at 550-600℃, which inhibits AlN grain boundary precipitation on the billet surface, refines the surface grains, and improves grain boundary bonding.

[0064] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. 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 this application. Therefore, this application 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 in this application.

Claims

1. A weathering steel plate, characterized in that, The chemical composition of the weathering steel plate, by mass percentage, comprises: C: 0.07%-0.11%, Si: 0.2%-0.6%, Mn: 0.3%-0.5%, Cu: 0.20%-0.40%, Ni: 0.01%-0.03%, Ti: 0.01%-0.02%, Zr: 0-0.01%, Cr: 0.20%-0.40%, P: 0.06%-0.12%, N: 0.002%-0.004%, with the remainder being Fe and unavoidable impurities; wherein the total content of Ti and Zr is 0.01%-0.03%.

2. The weathering steel plate according to claim 1, characterized in that, The microstructure of the weathering steel plate includes ferrite and pearlite; by volume percentage, the ferrite accounts for 80%-95% and the pearlite accounts for 5%-20% in the weathering steel plate; the grain size of both the ferrite and the pearlite is 5μm-10μm.

3. A method for preparing the weathering steel plate according to claim 1 or 2, characterized in that, Includes the following steps: Molten steel is provided, and the molten steel is smelted and continuously cast to obtain a continuously cast billet; The continuous casting billet is subjected to roller cooling treatment to obtain a pre-cooled continuous casting billet; the surface temperature of the pre-cooled continuous casting billet is 550℃-600℃. The pre-cooled continuous casting billet is heated to obtain a hot casting billet; The hot-cast billet is rolled to obtain a hot-rolled plate; The hot-rolled plate is cooled to obtain the weathering steel plate.

4. The method for preparing weathering steel plate according to claim 3, characterized in that, The roller cooling process includes spraying water onto the surface of the continuously cast billet located on the roller conveyor for 2-5 minutes using nozzles; the water flow velocity from the nozzles is 5-10 m / s.

5. The method for preparing weathering steel plate according to claim 3, characterized in that, The heat treatment includes heating the pre-cooled continuous casting billet to 1160℃-1190℃ and holding it at 1160℃-1190℃ for 160min-200min.

6. The method for preparing weathering steel plate according to claim 5, characterized in that, If the thickness of the hot-rolled plate is <4.0mm, the pre-cooled continuous casting billet is heated to 1170℃-1190℃ and held at 1170℃-1190℃ for 180min-200min during the heat treatment; if the thickness of the hot-rolled plate is ≥4.0mm, the pre-cooled continuous casting billet is heated to 1160℃-1180℃ and held at 1160℃-1180℃ for 160min-180min during the heat treatment.

7. The method for preparing weathering steel plate according to claim 3, characterized in that, The heating furnace atmosphere during the heat treatment is a weakly reducing atmosphere; the excess air coefficient in the heating furnace is 0.95-1.

0.

8. The method for preparing weathering steel plate according to claim 3, characterized in that, The rolling process includes sequentially performing rough rolling and finish rolling on the hot-cast billet; the rolling mills used in the rough rolling process include: a first rolling mill and a second rolling mill; when using the first rolling mill, the hot-cast billet is rolled three times; when using the second rolling mill, the hot-cast billet that has undergone the three rolling processes is rolled five times.

9. The method for preparing weathering steel plate according to claim 8, characterized in that, If the thickness of the hot-rolled plate is <4.0mm, the reduction in the width of the vertical roll of the vertical roll side press must be ≤60mm during the rough rolling process; if the thickness of the hot-rolled plate is ≥4.0mm, the reduction in the width of the vertical roll of the vertical roll side press must be ≤100mm during the heating process.

10. The method for preparing weathering steel plate according to claim 8, characterized in that, The exit temperature of the rough rolling process is 1050℃-1100℃.

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