Highly corrosion resistant weathering steels and method of making and use thereof

Abstract

The application discloses a high-corrosion-resistance weathering steel and a preparation method and application thereof. The high-corrosion-resistance weathering steel comprises, in percentage by weight, C: 0.10%-0.12%, Si: 0.10%-0.20%, Mn: 1.0%-1.8%, P: 0.075%-0.115%, S: ≤0.0015%, Cr: 0.45%-0.65%, Cu: 0.25%-0.50%, Al: 0.50%-0.75%, Ti: 0.07%-0.12%, Nb: 0.01%-0.04%, Ca: 0.0010%-0.0025%, N: ≤0.0045%, and the balance of Fe and other inevitable impurities. According to the embodiment of the application, the relative corrosion rate of the weathering steel can be improved, and the alloy cost can be reduced.

Description

Technical Field

[0001] This application relates to weathering steel, and more particularly to a high corrosion-resistant weathering steel, its preparation method, and its application. Background Technology

[0002] Weathering steel is a type of structural steel with resistance to atmospheric corrosion. It is a low-alloy steel made by adding certain amounts of alloying elements such as Cu, P, Cr, and N to ordinary steel. Based on the alloying elements, it can be classified into Cr-Ni-Cu, Cr-Ni-Cu-P, and Cr-Cu-P systems. In industrial and rural atmospheric environments, weathering steel exhibits excellent resistance to atmospheric corrosion because it forms a dense and stable protective oxide film on its surface, hindering the entry of corrosive media.

[0003] However, the current weathering steel has a relatively low corrosion rate; and the alloy cost required is high, making it not economically viable. Summary of the Invention

[0004] This application provides a high corrosion-resistant weathering steel, its preparation method, and its application, which can improve the relative corrosion rate of weathering steel while reducing the cost of alloying.

[0005] In a first aspect, embodiments of this application provide a weathering steel with high corrosion resistance, comprising, by weight percentage: C: 0.10%–0.12%, Si: 0.10%–0.20%, Mn: 1.0%–1.8%, P: 0.075%–0.115%, S: ≤0.0015%, Cr: 0.45%–0.65%, Cu: 0.25%–0.50%, Al: 0.50%–0.75%, Ti: 0.07%–0.12%, Nb: 0.01%–0.04%, Ca: 0.0010%–0.0025%, N: ≤0.0045%, with the balance being Fe and other unavoidable impurities.

[0006] In any embodiment of this application, the ratio of Ca to S content in the weathering steel is 1.0 to 2.5:1.

[0007] In any embodiment of this application, by weight percentage, the composition includes: C: 0.10%–0.12%, Si: 0.10%–0.20%, Mn: 1.0%–1.8%, P: 0.100%–0.115%, S: ≤0.0015%, Cr: 0.45%–0.65%, Cu: 0.25%–0.50%, Al: 0.700%–0.75%, Ti: 0.07%–0.12%, Nb: 0.01%–0.04%, Ca: 0.0010%–0.0025%, N: ≤0.0045%, with the balance being Fe and other unavoidable impurities.

[0008] In any embodiment of this application, the ferrite content in the microstructure of weathering steel is ≥90%.

[0009] In any embodiment of this application, the weathering steel has a yield strength ≥550MPa, tensile strength ≥700MPa, elongation ≥18%, yield strength ratio ≤0.85, and low-temperature impact at -40℃ ≥47J.

[0010] Secondly, embodiments of this application provide a method for preparing weathering steel, comprising: smelting materials containing a preset ratio of C, Si, Mn, P, S, Cr, Cu, Al, Ti, Nb, Ca, N and Fe into molten steel, and casting it into a slab; hot rolling the slab to obtain a steel strip, and then coiling it to obtain weathering steel; wherein, hot rolling includes a heating process, a rolling process and a laminar flow cooling process, and the laminar flow cooling process includes: cooling the rolled steel strip to the temperature range of ferrite transformation, then air cooling for more than 6 seconds, and finally cooling it to the target temperature range.

[0011] In any embodiment of this application, the laminar flow cooling process includes: cooling the rolled steel strip to 680-740°C at a cooling rate of 80-150°C / s, then air-cooling it to 660-720°C for more than 6s, and then cooling it to 520-600°C at a cooling rate of more than 20°C / s.

[0012] In any embodiment of this application, the thickness of the cast slab is 230–240 mm.

[0013] In any embodiment of this application, the heating process includes: placing the slab in a heating furnace for heating, wherein the slab's furnace entry temperature is ≤700℃, the slab's heating rate is ≥480℃ / h, the total furnace time for the slab is 160~350min, the slab's furnace exit temperature is 1200~1250℃, and the excess air coefficient of the heating atmosphere in the heating furnace is 1.1~1.5.

[0014] In any embodiment of this application, the heating process includes a preheating section, a first heating section, a second heating section, and a soaking section. The temperature of the preheating section is 900–1000°C, the temperature of the first heating section is 1190–1230°C, the temperature of the second heating section and the soaking section are both 1200–1250°C, and the total heat preservation time of the second heating section and the soaking section is ≥25 min.

[0015] In any embodiment of this application, the total holding time of the second heating section and the soaking section satisfies T≤(100-1.47×t) as well as the target thickness of the weathering steel. 2 ), where T is the total heat preservation time in minutes and t is the target thickness of the weathering steel in mm.

[0016] In any embodiment of this application, the rolling process includes sequentially roughing and finishing the slab after the heating process. In the roughing process, the total reduction rate is ≥75%, the reduction rate of the first stand is ≥20%, the reduction rate of the last stand is ≥30%, and the finishing temperature is 1060~1110℃. In the finishing process, the starting temperature is ≤1090℃, the reduction rate of the last stand is ≥10%, and the finishing temperature is 880~930℃.

[0017] In any embodiment of this application, the thickness after the final rolling pass of the roughing mill is 38–48 mm.

[0018] In any embodiment of this application, when the thickness after rolling of the last stand of the finishing mill is <3.0 mm, the final rolling temperature is 910-930℃; when the thickness after rolling of the last stand of the finishing mill is 3.0-4.0 mm, the final rolling temperature is 900-920℃; when the thickness after rolling of the last stand of the finishing mill is >4.0 mm, the final rolling temperature is 880-900℃.

[0019] Thirdly, the embodiments of this application provide the application of the weathering steel described above or the weathering steel obtained by the above preparation method in containers, highway guardrails, and outdoor structural steel.

[0020] The high corrosion-resistant weathering steel, its preparation method, and its application, as described in this application, can promote the formation of a protective rust layer on the surface of weathering steel by adding a high content of phosphorus (P), effectively improving the atmospheric corrosion resistance of the weathering steel. By adding a high content of aluminum (Al), the AlOOH and Al(OH)3 generated in the weathering steel can form large-sized aluminum-rich particles, thereby filling pores and cracks, improving the density of the rust layer, and aluminum is concentrated in Al... 3+ Ar3 exists in the form of composite oxides in the inner rust layer and accumulates there, increasing corrosion resistance and effectively inhibiting corrosion. Simultaneously, the high Al content increases the ferrite content to offset the problems of center segregation and grain boundary segregation caused by the high P content. Furthermore, by reducing the Cr content, the addition of precious elements such as V, Ni, Mo, and W is avoided, thus reducing alloy costs. Additionally, by controlling the contents of C, Si, Mn, P, S, Cr, Cu, Al, Ti, Nb, Ca, and N, the Ar3 temperature is kept ≤890℃ to improve production stability. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1Metallographic image of the weathering steel prepared in Example 3 of this application;

[0023] Figure 2 This is a flowchart illustrating the preparation process of some embodiments of this application. Detailed Implementation

[0024] To better understand the above-mentioned objectives, features, and advantages of this application, the solution of this application will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0025] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this application may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of this application, and not all embodiments.

[0026] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the high corrosion-resistant weathering steel, its preparation method, and its applications. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0027] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0028] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0029] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0030] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0031] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0032] Unless otherwise specified, this application uses conventional testing methods or testing methods recommended by the instrument.

[0033] The yield strength ratio is the ratio of a material's yield point (yield strength) to its tensile strength. A yield strength ratio that is too high leads to brittle failure, where no obvious deformation occurs, making it impossible to detect and prevent in advance. A higher yield strength ratio generally results in better mechanical parts (considering material savings and weight reduction). The yield strength ratio can be seen as a coefficient for measuring the strength reserve of steel.

[0034] Ar3 temperature refers to the temperature at which proeutectoid ferrite begins to precipitate from austenite during cooling.

[0035] AC3 temperature refers to the temperature at which all proeutectoid ferrite transforms into austenite during heating.

[0036] Weather resistance index: The weather resistance index can evaluate the weather resistance of steel. Generally, a weather resistance index ≥ 6.0 is sufficient for use without painting.

[0037] The excess air coefficient is the ratio of the actual air requirement to the theoretical air requirement during fuel combustion.

[0038] High corrosion-resistant weathering steel

[0039] This application provides a high corrosion-resistant weathering steel, comprising, by weight percentage: C: 0.10%–0.12%, Si: 0.10%–0.20%, Mn: 1.0%–1.8%, P: 0.075%–0.115%, S: ≤0.0015%, Cr: 0.45%–0.65%, Cu: 0.25%–0.50%, Al: 0.50%–0.75%, Ti: 0.07%–0.12%, Nb: 0.01%–0.04%, Ca: 0.0010%–0.0025%, N: ≤0.0045%, with the balance being Fe and other unavoidable impurities.

[0040] This application controls the carbon content to 0.10%–0.12%, which balances the control of steel microstructure and production process. Carbon is a very inexpensive strengthening element for steel. If the chromium content in weathering steel is high, the high carbon content will easily form martensite in the steel, reducing its ductility and toughness, increasing its tensile strength, and ultimately leading to cracking during processing. Increasing the carbon content also reduces the corrosion resistance of the steel. Because this application adds a high content of Al, a strong ferrite strengthening element that can significantly increase the AC3 temperature of the steel, the coarsened steel microstructure is not conducive to hot rolling process control. Conversely, carbon is a strong austenite forming element and can lower the AC3 temperature of the steel.

[0041] Optionally, the weight percentage of C is independently selected from any value or a range between 0.100%, 0.102%, 0.104%, 0.106%, 0.108%, 0.110%, 0.112%, 0.114%, 0.115%, 0.118%, 0.120%.

[0042] In this application, the Si content of 0.10% to 0.20% can exist in solid solution within ferrite and austenite to improve the strength of the steel and reduce the overall corrosion rate. However, during hot rolling, higher Si content easily produces obvious red iron oxide scale defects on the strip surface, which are difficult to remove by descaling, affecting the surface quality of the strip. In addition, as the Si content increases, the rust layer becomes loose and porous, reducing the corrosion resistance of the steel.

[0043] Optionally, the weight percentage of Si is independently selected from any value or a range between 0.100%, 0.102%, 0.105%, 0.106%, 0.108%, 0.110%, 0.112%, 0.114%, 0.115%, 0.118%, 0.120%, 0.125%, 0.145%, 0.175%, and 0.200%.

[0044] In this application, a Mn content of 1.0% to 1.8% can expand the austenite region in the iron-carbon phase diagram, promote the mid-temperature microstructure transformation, and is beneficial for microstructure refinement and improving the strength and low-temperature toughness of the steel. However, excessive Mn content will cause severe segregation in the steel, deteriorating the low-temperature toughness of the steel.

[0045] Optionally, the weight percentage of Mn is independently selected from any value of 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, or a range between any two.

[0046] Phosphorus (P) can be added to weathering steel as a corrosion-resistant element, promoting the formation of a protective rust layer and effectively improving the steel's resistance to atmospheric corrosion. When the P content in steel exceeds 0.07%, its corrosion resistance can be significantly improved. However, P is also a harmful element in steel, easily segregating in the center of the thickness during continuous casting of steel billets. Simultaneously, P tends to agglomerate at grain boundaries, reducing grain boundary bonding energy and thus decreasing the steel's toughness and plasticity. This application improves the corrosion resistance of steel by adding 0.075% to 0.115% P. Simultaneously, by controlling the ferrite content in the steel to over 90%, the microstructure is refined, the low-temperature toughness of the steel is improved, and defects caused by P are suppressed.

[0047] Optionally, the weight percentage of P is independently selected from any value or a range between 0.075%, 0.078%, 0.080%, 0.082%, 0.085%, 0.087%, 0.089%, 0.090%, 0.100%, 0.102%, 0.104%, 0.106%, 0.108%, 0.110%, 0.112%, and 0.115%.

[0048] In this application, the sulfur content is ≤0.0015%, which can reduce the adverse effects of sulfur on the corrosion resistance, cold forming performance, low-temperature toughness, and weldability of steel.

[0049] Optionally, the weight percentage of S is independently selected from any value among 0.0007%, 0.0009%, 0.0010%, 0.0012%, 0.0013%, 0.0014%, 0.0015%, or a range between any two.

[0050] In this application, the Cr content is 0.45% to 0.65%, lower than that in existing weathering steels. This allows for the formation of a dense oxide film on the steel surface, improving its passivation ability and reducing alloy costs. When Cr and Cu are added to the steel simultaneously, a synergistic effect occurs, further enhancing the passivation energy. A high Cr content is beneficial for refining α-FeOOH; additionally, Cr can also enable the steel to form bainite or martensite at lower cooling rates.

[0051] Optionally, the weight percentage of Cr is independently selected from any value or a range between 0.45%, 0.46%, 0.47%, 0.48%, 0.49%, 0.50%, 0.51%, 0.52%, 0.53%, 0.54%, 0.55%, 0.56%, 0.57%, 0.60%, 0.61%, 0.62%, 0.63%, 0.64%, and 0.65%.

[0052] In this application, the Cu content is 0.25%–0.50%, which can act as an active cathode. Under certain conditions, it can promote anodic passivation of steel, thereby reducing the corrosion rate. Alternatively, Cu enrichment in the rust layer can improve the protective performance of the rust layer, thus enhancing the corrosion resistance of the steel. The combined effect of Cu and P can promote the formation of extremely dense amorphous Fe3O4 in the rust layer, thereby preventing oxygen and water from penetrating into the steel matrix. Cu can also react with S to form insoluble compounds that block cracks in the rust layer.

[0053] Optionally, the weight percentage of Cu is independently selected from any value or a range between 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.37%, 0.39%, 0.40%, 0.42%, 0.44%, 0.45%, 0.46%, 0.47%, 0.48%, 0.49%, and 0.50%.

[0054] In this application, the Al content is 0.50% to 0.75%, which can improve the corrosion resistance of steel. Large-sized aluminum-rich particles composed of AlOOH and Al(OH)3 can fill pores and cracks, improving the density of the rust layer. Al... 3+ The composite oxides present in the inner rust layer and enriched there increase corrosion resistance, effectively inhibiting corrosion. Simultaneously, Al strengthens ferrite, inhibits corrosion product crystallization, and promotes the formation of protective fine-grained corrosion products, thus suppressing the transformation of ferrite to pearlite and improving the steel's corrosion resistance. Cr-Al exhibits excellent resistance to both atmospheric and seawater corrosion; its corrosion products are denser than those of ordinary carbon steel, and its electrochemical corrosion resistance is 3-4 times that of ordinary carbon steel. High Al and Si contents increase the temperature of Ar3, while C and Mn decrease it. By controlling the contents of C, Si, Mn, P, S, Cr, Cu, Al, Ti, Nb, Ca, and N, the temperature of Ar3 can be kept ≤890℃, overcoming problems such as grain coarsening caused by high Al content, thereby improving the stability of weathering steel production.

[0055] Optionally, the weight percentage of Al is independently selected from any value or a range between 0.50%, 0.51%, 0.52%, 0.53%, 0.54%, 0.55%, 0.56%, 0.57%, 0.60%, 0.61%, 0.62%, 0.63%, 0.64%, 0.65%, 0.66%, 0.67%, 0.68%, 0.69%, 0.70%, 0.71%, 0.72%, 0.73%, 0.74%, and 0.75%.

[0056] In this application, the Ti content is 0.07% to 0.12%, which can improve the material's resistance to intergranular corrosion. Ti can combine with N in the steel to improve the cleanliness of the steel, and can also form nanoscale TiC or precipitate in the form of Ti(C,N) second phase particles.

[0057] Optionally, the weight percentage of Ti is independently selected from any value or a range between 0.070%, 0.075%, 0.080%, 0.083%, 0.085%, 0.088%, 0.090%, 0.095%, 0.100%, 0.105%, 0.110%, 0.115%, and 0.120%.

[0058] In this application, the Nb content is 0.01% to 0.04%. It can strengthen the matrix by solid solution in the steel matrix or by combining with carbon and nitrogen in the steel to form carbonitrides. For example, carbonitrides of undissolved Nb during high-temperature homogenization can prevent austenite grain growth. Nb precipitated by deformation during solid solution or rolling can inhibit the recrystallization of deformed austenite and significantly refine the recrystallized grains. Nb precipitated during subsequent ferrite phase transformation can play a good precipitation strengthening role.

[0059] In this application, the N content is ≤0.0045%, which can consume Ti and form inclusions, so N needs to be controlled at a low level.

[0060] In this application, the Ca content is 0.0010% to 0.0025%. Through the inclusion modification effect of Ca, MnS and Al2O3 inclusions in the steel can be transformed into spherical inclusions containing Ca-Al-Mn-OS. With increasing Ca content, the inclusions in the steel tend to be more diffusely and uniformly distributed, thereby improving the quality of the steel. Within this range, the rust layer of Ca-containing weathering steel is very dense, with few cracks and pores, and the thickness of the protective rust layer increases significantly, providing good protection for the substrate. Ca alloying in weathering steel can promote the formation of a stable and dense α-FeOOH phase in the rust layer. Simultaneously, Ca can promote the uniform enrichment of the alloying element Cu throughout the rust layer, which is beneficial for the formation of the protective rust layer.

[0061] In this application, the Ca to S content ratio is 1.0 to 2.5, which can make inclusions in the steel tend to be evenly distributed, thus improving the quality of the steel. At the same time, it can reduce the contamination of molten steel.

[0062] In some embodiments, the ratio of Ca to S content in weathering steel is 1.0 to 2.5:1.

[0063] Optionally, the Ca to S content ratio in the weathering steel is independently selected from any value among 1.0:1, 1.2:1, 1.5:1, 1.7:1, 2.0:1, 2.2:1, 2.5:1 or any range between the two.

[0064] In some embodiments, the composition, by weight percentage, includes: C: 0.10%–0.12%, Si: 0.10%–0.20%, Mn: 1.0%–1.8%, P: 0.100%–0.115%, S: ≤0.0015%, Cr: 0.45%–0.65%, Cu: 0.25%–0.50%, Al: 0.700%–0.75%, Ti: 0.07%–0.12%, Nb: 0.01%–0.04%, Ca: 0.0010%–0.0025%, N: ≤0.0045%, with the balance being Fe and other unavoidable impurities. Weathering steel with this composition, having a higher content of P and Al, can better improve the corrosion resistance of weathering steel, while simultaneously giving it excellent elongation and a low yield strength ratio (≤0.85), and excellent complex cold-working properties.

[0065] In some embodiments, the ferrite content in the microstructure of weathering steel is ≥90%.

[0066] Ferrite is a type of metallographic structure, referring to an interstitial solid solution of carbon dissolved in α-Fe, commonly represented by F. Ferrite has a very low carbon content, and its properties are close to those of pure iron. It is a structure with high plasticity and toughness, and low strength and hardness.

[0067] The ferrite content in this application is ≥90%, which can offset the problems of central segregation and grain boundary segregation caused by high P content, thereby enabling the weathering steel to have high low-temperature impact performance, high elongation and low yield strength ratio (≤0.85), and giving the steel excellent complex forming ability.

[0068] In some embodiments, the grain size of weathering steel is grade 10 or higher. Grain size is a measure of grain size. Commonly used methods of representation include the number of grains per unit volume (ZV), the number of grains per unit area (ZS), or the average linear length (or diameter) of the grains. In industrial production, grain size grades are used to represent grain size. Standard grain size is divided into 12 grades: grades 1-4 are coarse grains, grades 5-8 are fine grains, and grades 9-12 are ultrafine grains.

[0069] The grain size of the weathering steel in this application is above grade 10, which can improve the yield strength, plasticity and toughness.

[0070] In some embodiments, the weathering steel has an upper yield strength ≥550MPa, tensile strength ≥670MPa, elongation ≥18%, low-temperature impact energy ≥47J at -40℃, passes cold bending at 180°D=1t, and yield strength ratio ≤0.85.

[0071] In some embodiments, the relative corrosion rate of weathering steel in the cyclic immersion corrosion test is ≤35% compared to Q355B low-alloy structural steel, and the weathering index I of the steel is ≥6.5. Q355B refers to the steel grade, which is composed of the first letters of the Chinese pinyin for "yield strength," "high weather resistance," or "weathering," such as "Q," "GNH," or "NH," the lower limit of the yield strength, and the quality grade (A, B, C, D, E).

[0072] In some embodiments, the Ar3 temperature of weathering steel is ≤890°C. Weathering steel within this range can improve production stability.

[0073]

Preparation Method

[0074] This application provides a method for preparing weathering steel, including: S10, smelting materials containing a preset ratio of C, Si, Mn, P, S, Cr, Cu, Al, Ti, Nb, Ca, N and Fe into molten steel and casting it into a slab; S20, hot rolling the slab to obtain a steel strip, and then coiling it to obtain weathering steel; wherein, hot rolling includes a heating process, a rolling process and a laminar flow cooling process, and the laminar flow cooling process includes: cooling the rolled steel strip to the temperature range of ferrite transformation, then air cooling for more than 6 seconds, and finally cooling it to the target temperature range.

[0075] This application utilizes a laminar flow cooling process, which involves first cooling the rolled steel strip to the temperature range for ferrite transformation, then air cooling for more than 6 seconds, and finally cooling it to the target temperature range. This process can promote ferrite transformation and increase the proportion of ferrite in weathering steel.

[0076] like Figure 2 As shown, a method for preparing weathering steel includes: smelting and continuously casting materials containing a predetermined ratio of C, Si, Mn, P, S, Cr, Cu, Al, Ti, Nb, Ca, N, and Fe to obtain a weathering steel slab; heating the slab, rough descaling, rough rolling, and cooling the intermediate slab to obtain an intermediate slab; cutting off the intermediate slab, fine descaling, fine rolling, ultra-rapid cooling, concentrated cooling in the later stage, coiling, and slow cooling to obtain the final weathering steel.

[0077] In some embodiments, the laminar flow cooling process includes: cooling the rolled steel strip to 680-740°C at a cooling rate of 80-150°C / s, then air-cooling it to 660-720°C for more than 6s, and then cooling it to 520-600°C at a cooling rate of more than 20°C / s.

[0078] In hot rolling, to control the cooling rate of the strip (the rolled slab is called strip or steel strip), laminar flow cooling production lines are generally quite long, with multiple sets of manifolds (for water cooling of the strip). Water can be continuously supplied to adjacent manifolds (called centralized cooling) or intermittently supplied to manifolds (called sparse cooling). This water cooling method can be used at the beginning or end of the laminar flow cooling process. If no water is supplied to the manifolds, air is used for cooling, which is called air cooling.

[0079] This application cools the strip steel (rolled slab) to 680-740℃ at a cooling rate of 80-150℃ / s, i.e., using an ultra-fast cooling method to reduce the temperature to the ferrite transformation temperature range in a shorter time and distance, thus allowing time for air cooling. The strip steel then enters an air-cooling section for air cooling for ≥6s; sufficient air cooling time can improve ferrite transformation. After air cooling to 660-720℃, the strip steel undergoes concentrated cooling in the later section at a cooling rate ≥20℃ / s to 520-600℃. Finally, it is coiled, with the strip steel head and tail using a U-shaped cooling process. The coiling temperature at 0-20m from each head and tail is 580-620℃ to improve the overall coil performance stability. The head and tail of the strip steel have a larger contact area with air and are in an air-cooled state compared to the strip body; the strip body is located inside the coil, and its cooling method is relatively slow. Generally, the yield strength and elongation of slowly cooled strip steel are higher than those of air-cooled strip steel. To reduce the impact on product performance caused by the higher cooling rate of the inner and outer rings of the strip (i.e., the head and tail of the strip) due to contact with air compared to the middle of the strip, a certain amount of temperature compensation is applied within a certain length of the head and tail of the strip, based on the target coiling temperature. The target coiling temperature at the head and tail of the strip is higher than that at the middle of the strip.

[0080] In some embodiments, the thickness of the cast slab is 230–240 mm.

[0081] Optionally, the thickness of the cast slab is independently selected from any value or a range between 230 mm, 231 mm, 232 mm, 233 mm, 234 mm, 235 mm, 236 mm, 237 mm, 238 mm, 239 mm, and 240 mm.

[0082] In some embodiments, the heating process includes: placing the slab in a heating furnace for heating, wherein the slab's furnace entry temperature is ≤700℃, the slab's heating rate is ≥480℃ / h, the total furnace time for the slab is 160~350min, the slab's furnace exit temperature is 1200~1250℃, and the excess air coefficient of the heating atmosphere in the heating furnace is 1.1~1.5.

[0083] Optionally, the furnace entry temperature of the slab is independently selected from any value or a range between any two of 300℃, 350℃, 370℃, 400℃, 417℃, 450℃, 470℃, 500℃, 532℃, 550℃, 578℃, 600℃, 614℃, 650℃, and 700℃.

[0084] Optionally, the heating rate of the slab is independently selected from 480℃ / h, 496℃ / h, 500℃ / h,

[0085] 515℃ / h, 532℃ / h, 550℃ / h, 560℃ / h, 570℃ / h, 578℃ / h, 600℃ / h,

[0086] Any value between 650℃ / h and 700℃ / h, or any range between the two.

[0087] Optionally, the total time the slab spends in the furnace is independently selected from any value or a range between 160 min, 180 min, 200 min, 217 min, 230 min, 241 min, 270 min, 286 min, 300 min, 320 min, 340 min, and 350 min.

[0088] Optionally, the furnace exit temperature of the slab is independently selected from any value or a range between 1200℃, 1204℃, 1210℃, 1211℃, 1214℃, 1220℃, 1236℃, 1240℃, 1245℃, and 1250℃.

[0089] In some embodiments, the heating process includes a preheating section, a first heating section, a second heating section, and a soaking section. The temperature of the preheating section is 900–1000°C, the temperature of the first heating section is 1190–1230°C, the temperatures of the second heating section and the soaking section are both 1200–1250°C, and the total holding time of the second heating section and the soaking section is ≥25 min.

[0090] Optionally, the temperatures of the second heating section and the soaking section are independently selected from any value or a range between 1200℃, 1204℃, 1208℃, 1211℃, 1214℃, 1220℃, 1226℃, 1243℃, 1245℃, and 1250℃.

[0091] Optionally, the total holding time of the second heating section and the heat soaking section is independently selected from any value or a range between 25 min, 30 min, 35 min, 37 min, 39 min, 40 min, 43 min, 45 min, 50 min, 52 min, and 60 min.

[0092] In some embodiments, the total holding time of the second heating section and the soaking section satisfies T≤(100-1.47×t) as well as the target thickness of the weathering steel. 2 ), where T is the total heat preservation time in minutes and t is the target thickness of the weathering steel in mm.

[0093] In some embodiments, the rolling process includes sequentially roughing and finishing the slab after the heating process. In the roughing process, the total reduction rate is ≥75%, the reduction rate of the first stand is ≥20%, the reduction rate of the last stand is ≥30%, and the finishing temperature is 1060~1110℃. In the finishing process, the starting temperature is ≤1090℃, the reduction rate of the last stand is ≥10%, and the finishing temperature is 880~930℃.

[0094] In some embodiments, the thickness after the final pass of roughing rolling is 38–48 mm.

[0095] In some embodiments, when the thickness after rolling the last stand of the finishing mill is <3.0 mm, the final rolling temperature is 910–930°C; when the thickness after rolling the last stand of the finishing mill is 3.0–4.0 mm, the final rolling temperature is 900–920°C; and when the thickness after rolling the last stand of the finishing mill is >4.0 mm, the final rolling temperature is 880–900°C.

[0096] Thirdly, the embodiments of this application provide the application of the weathering steel described above or the weathering steel obtained by the above preparation method in containers, highway guardrails, and outdoor structural steel.

[0097] Examples 1-4

[0098] 1. Smelt steel according to the composition shown in Table 1 and cast it into slabs. The thickness of the slabs is shown in Table 3.

[0099] 2. The slab from step 1 is placed in the heating furnace of a conventional hot rolling line for heating. It is heated in stages through the preheating section and the first heating section, and reaches the holding temperature in the second heating section and the soaking section. The holding temperature, holding time, slab entry temperature, slab heating rate, total slab time in the furnace, exit temperature, and excess air coefficient of the heating atmosphere in the furnace are shown in Table 2.

[0100] 3. The slab after heat preservation in step 2 is subjected to rough descaling, followed by rough rolling. After cooling, an intermediate slab is obtained. The intermediate slab is then subjected to head cutting, fine descaling, fine rolling, ultra-rapid cooling, concentrated cooling at the rear, coiling, and slow cooling to obtain the final weathering steel. The parameters for rough rolling, fine rolling, ultra-rapid cooling, concentrated cooling at the rear, coiling, and slow cooling are shown in Tables 3 and 4.

[0101] Table 1. Chemical composition of weathering steel in different embodiments

[0102]

[0103] The formula for calculating the weather resistance index I in Table 1 is as follows:

[0104] I=26.01(%Cu)+3.88(%Ni)+1.2(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.1(%Ni)(%P)-33.39(%Cu) 2

[0105] In the formula: (%Cu), (%Ni), (%Cr), (%Si), (%P) represent the content of each element.

[0106] Table 2 Heating processes of different embodiments

[0107]

[0108] Table 3 Rolling processes of different embodiments

[0109]

[0110] Table 4 Cooling processes of different embodiments

[0111]

[0112] Data Analysis

[0113] The mechanical and corrosion properties of the weathering steel and plain carbon steel Q355B prepared in Examples 1-4 were tested.

[0114] The corrosion performance was compared with that of ordinary carbon steel Q355B after 72 hours of immersion corrosion, according to TB / T2375-93. The mechanical properties were tested according to "GB 228.3 Tensile Testing Part 3 Low Temperature Test Method". The specific results are shown in the table below.

[0115] Table 5

[0116]

[0117] Because the steel plates in Examples 1-3 were thin, no impact performance tests were conducted. Only the steel plate in Example 4 underwent an impact test.

[0118] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A weathering steel having high corrosion resistance, characterized by, comprises, by weight percentage: C: 0.10%~0.12%, Si: 0.10%~0.20%, Mn: 1.0%~1.8%, P: 0.075%~0.115%, S: ≤0.0015%, Cr: 0.45%~0.65%, Cu: 0.25%~0.50%, Al: 0.50%~0.75%, Ti: 0.07%~0.12%, Nb: 0.01%~0.04%, Ca: 0.0010%~0.0025%, N: ≤0.0045%, the balance being Fe and other unavoidable impurities; The preparation method of the weathering steel comprises: melting materials containing preset proportions of C, Si, Mn, P, S, Cr, Cu, Al, Ti, Nb, Ca, N and Fe into molten steel, and casting into a slab; hot rolling the slab to obtain a steel strip, and then coiling to obtain the weathering steel; The hot rolling comprises a heating process, a rolling process and a laminar cooling process, The heating process comprises: placing the slab in a heating furnace for heating, the slab has an entering temperature ≤700 ℃, the slab has a temperature rising speed ≥480 ℃ / h, the total time of the slab in the furnace is 160-350 min, the slab has an exiting temperature of 1200-1250 ℃, and the air excess coefficient of the heating atmosphere in the heating furnace is 1.1-1.5; the heating process comprises a preheating section, a first heating section, a second heating section and a soaking section, the preheating section has a temperature of 900-1000 ℃, the first heating section has a temperature of 1190-1230 ℃, the second heating section and the soaking section both have a temperature of 1200-1250 ℃, and the total time of the second heating section and the soaking section for heat preservation is ≥25 min; the total time of the second heating section and the soaking section for heat preservation and the target thickness of the weathering-resistant steel satisfy T ≤ (100-1.47×t 2 ), wherein T is the total time for heat preservation, in min, and t is the target thickness of the weathering-resistant steel, in mm. The rolling process comprises sequentially rough rolling and finish rolling the slab after the heating process, in the rough rolling, the total reduction of the rough rolling is ≥75%, the first pass rolling reduction of the rough rolling is ≥20%, the last pass rolling reduction of the rough rolling is ≥30%, and the finish rolling temperature of the rough rolling is 1060~1110 ℃; in the finish rolling, the finish rolling inlet temperature is ≤1090 ℃, the last pass rolling reduction is ≥10%, and the finish rolling temperature is 880~930 ℃; the thickness after the last pass rolling of the rough rolling is 38~48 mm; when the thickness after the last pass rolling of the finish rolling is <3.0 mm, the finish rolling temperature is 910~930 ℃; when the thickness after the last pass rolling of the finish rolling is 3.0~4.0 mm, the finish rolling temperature is 900~920 ℃; and when the thickness after the last pass rolling of the finish rolling is >4.0 mm, the finish rolling temperature is 880~900 ℃; The laminar cooling process comprises: cooling the rolled steel strip to 680~740 ℃ at a cooling speed of 80~150 ℃ / s, then air cooling for 6 s or more to 660~720 ℃, and then cooling to 520~600 ℃ at a cooling speed of 20 ℃ / s or more.

2. Weathering steel according to claim 1, characterized in that The content ratio of Ca to S in the weathering steel is 1.0~2.5:

1.

3. The weathering steel according to claim 1, characterized in that comprises, by weight percentage: C: 0.10%~0.12%, Si: 0.10%~0.20%, Mn: 1.0%~1.8%, P: 0.100%~0.115%, S: ≤0.0015%, Cr: 0.45%~0.65%, Cu: 0.25%~0.50%, Al: 0.700%~0.75%, Ti: 0.07%~0.12%, Nb: 0.01%~0.04%, Ca: 0.0010%~0.0025%, N: ≤0.0045%, the balance being Fe and other unavoidable impurities.

4. The weathering steel according to claim 1, characterized in that In the metallographic structure of the weathering steel, the ferrite content ratio is ≥90%. And / or, the weathering steel has a yield strength ≥550 MPa, tensile strength ≥700 MPa, elongation ≥18%, yield strength ratio ≤0.85, and low-temperature impact strength ≥47 J at -40℃.

5. The weathering steel according to claim 1, characterized in that The thickness of the cast slab is 230~240 mm.

6. The application of weathering steel according to any one of claims 1-5 in containers, highway guardrails, and outdoor structural steel.

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