High-strength aluminized plate strip for corrosion-resistant structures and method for producing same

Abstract

A high-strength aluminum-clad steel strip for corrosion-resistant structures and its production method are disclosed. The strip comprises a steel strip and an aluminum strip. The steel strip has the following chemical composition by weight percentage: C 0.04–0.09%, 0 < Si ≤ 0.005%, Mn 0.4–0.8%, P 0.008–0.020%, S ≤ 0.008%, 0 < Al ≤ 0.005%, N 0.012–0.030%, 0 < O ≤ 0.01%, B 0.0005–0.002%, and selectively added Ti 0.01–0.06%, Nb 0.01–0.03%, Cu 0.01–0.15%, Cr 0.03–0.60%, and Ca. One or more of the following components are present in the range of 0.001% to 0.004%, with the balance including Fe and other unavoidable impurities; and must simultaneously satisfy the following: 0.5C + 3.83N + O - 0.89Al - 1.15Si ≥ 0.08; 150(C - 0.01) + 60P + 300N + 5Mn ≥ 13.0. Aluminum-clad sheets and strips possess excellent steel-aluminum bonding properties, stamping and deep-drawing performance, and surface quality. They can withstand high-temperature nitriding or other high-temperature treatments while maintaining good steel-aluminum bonding properties and cold-bending performance.

Description

Technical Field

[0001] This invention belongs to the field of low alloy steel manufacturing, specifically relating to a high-strength aluminum-coated steel strip for corrosion-resistant structures and its production method. Background Technology

[0002] Aluminum-clad steel sheets and strips are composite strip materials formed by rolling an aluminum layer onto the surface of steel strip at room temperature. Structurally, they can be steel-aluminum, steel-aluminum-steel, or aluminum-steel-aluminum. Aluminum-clad steel sheets and strips combine the strength of steel with the excellent heat dissipation, corrosion resistance, light weight, and aesthetic appeal of aluminum. Compared to pure aluminum, they significantly reduce costs, leading to their widespread application in radiator fins, corrosion-resistant pipes, and appliance panels. Their use is also expanding into automotive engine guards, new energy vehicle components, atmospheric corrosion resistant materials, cookware, and construction.

[0003] To extend service life, current container panels mostly use weathering steel, which requires the addition of numerous corrosion-resistant alloying elements to its composition. Simultaneously, to achieve high strength and weight reduction, reinforcing elements such as Ti and Nb are also added, significantly increasing costs. Furthermore, weathering steel provides overall corrosion resistance, while corrosion in steel structures primarily occurs on the material surface. The numerous corrosion-resistant alloys added internally to the steel plate cannot fully function, representing a waste of resources.

[0004] Aluminum is not only lightweight, aesthetically pleasing, and has good heat dissipation, but it also possesses excellent corrosion resistance in atmospheric environments. As a reactive metal, aluminum readily reacts with oxygen in the air to form aluminum oxide, creating a dense film on the surface at a thickness of only a few micrometers, which hinders further corrosion. In industrial atmospheric environments, the corrosion rate of aluminum is approximately 1 μm / a, and its corrosion resistance is about 10 times that of conventional atmospheric corrosion-resistant steel. Therefore, using aluminum-clad laminates to manufacture container panels and corrosion-resistant components not only provides excellent corrosion resistance but also results in an aesthetically pleasing surface. Since aluminum surfaces do not require painting, the painting process is reduced, lowering costs and making it more energy-efficient and environmentally friendly.

[0005] Chinese patent CN101660087 discloses "an aluminum-steel-aluminum composite material and its preparation method," which involves surface-treating aluminum and steel, then cold-rolling them into high-precision aluminum strips and steel strips respectively, followed by another cold rolling into a high-precision aluminum-steel-aluminum composite strip, and annealing it at 650–850℃ for 1–4 hours. Since aluminum's melting point is approximately 640℃, annealing at such a high temperature severely deteriorates the interfacial bonding strength between steel and aluminum. This fails to meet the performance and surface quality requirements of current applications of aluminum-clad laminates and strips.

[0006] Chinese patent CN102019727 discloses "aluminum-coated steel strip for coolers and its preparation method and the steel strip and aluminum alloy strip used therein". This patent mainly relates to aluminum-coated steel strips used for heat dissipation and the substrates used therein, with a width not exceeding 500 μm.

[0007] Chinese patents CN107881410A and CN108796384A disclose "An Aluminum-Clad Strip with Excellent Heat Dissipation and Its Production Method Thereof". The aluminum-clad materials involved in these patents are mainly used in the production of radiator fins and appliance panels, with a width not exceeding 500 μm, and relatively low strength. Therefore, these two patents differ significantly from this invention in terms of function and application.

[0008] Chinese patent CN107781426A discloses a "high-strength aluminum-clad sheet and strip and its manufacturing method," which ensures the steel-aluminum bonding performance of the aluminum-clad sheet and strip by controlling N, O, Si, and Al, and achieves a yield strength of 280-400 MPa. However, it contains up to 0.05% O (oxygen), which leads to numerous defects such as porosity and slag inclusions inside and on the surface of the cast billet, increasing the difficulty of billet cleaning and making the strip surface prone to peeling defects, thus reducing the yield. Furthermore, the aluminum-clad sheet and strip described in this application suffers from insufficient width, resulting in multiple splicing passes and low production efficiency when used in the processing of corrosion-resistant components such as containers, thus increasing production costs.

[0009] Chinese patent CN114250411A discloses "An Aluminum-Clad Plate and Strip for Kitchenware and Its Production Method." The aluminum-clad plate and strip used in wok manufacturing also involves nitriding during processing and specifies strength requirements after nitriding. However, this patent only requires a tensile strength ≥320MPa, while the yield strength and tensile strength of the substrate used are ≤280MPa and 380MPa respectively, significantly lower than those of this invention. Furthermore, the steel strip involved in this patent requires the carbon content to be controlled below 0.005%, and limits the P and S contents to no more than 0.012% and 0.006% respectively, increasing the difficulty of steelmaking and production costs. In terms of application, this application is limited to the processing of aluminum-clad materials for woks, with the aluminum layer thickness accounting for approximately 40-60% of the total thickness; and the width of the produced plate and strip does not exceed 460mm.

[0010] The comparison results show that existing steel-aluminum composite strips either have poor steel-aluminum bonding performance or do not meet high strength requirements. In particular, their width is generally no more than 500mm, and they are mainly used in the fields of radiator fins, home appliance panels, and food trays, mainly taking advantage of the high heat dissipation coefficient of aluminum. Summary of the Invention

[0011] The purpose of this invention is to provide a high-strength aluminum-coated sheet / strip for corrosion-resistant structures and its production method. The aluminum-coated sheet / strip possesses high strength, excellent steel-aluminum bonding performance, stamping and deep-drawing properties, and surface quality. Its yield strength is ≥350MPa, tensile strength ≥420MPa, and elongation A50 ≥18%, while maintaining good cold-bending performance, meeting the requirements of D=1a and 180° cold bending. The product is suitable for the production and processing of high-strength corrosion-resistant structures, featuring corrosion resistance, good heat dissipation, ease of cold forming, attractive appearance, and no need for painting.

[0012] To achieve the above objectives, the technical solution of the present invention is as follows:

[0013] A high-strength aluminum-clad steel strip for corrosion-resistant structures is a composite of steel and aluminum strips. The steel strip has the following chemical composition by weight percentage: C: 0.04–0.09%, 0 < Si ≤ 0.005%, Mn: 0.4–0.8%, P: 0.008–0.020%, S ≤ 0.008%, 0 < Al ≤ 0.005%, N: 0.012–0.030%, 0 < O ≤ 0.01%, B: 0.0005–0.002%, and optionally one or more of the following: Ti: 0.01–0.06%, Nb: 0.01–0.03%, Cu: 0.01–0.15%, Cr: 0.03–0.60%, Ca: 0.001–0.004%, with the balance including Fe and other unavoidable impurities; and simultaneously satisfying the following:

[0014] 0.5C+3.83N+O-0.89Al-1.15Si≥0.08;

[0015] 150(C-0.01)+60P+300N+5Mn≥13.0.

[0016] Furthermore, the balance consists of Fe and other unavoidable impurities.

[0017] The steel strip of this invention has a yield strength ≥300MPa, a tensile strength ≥360MPa, and an elongation ≥30%.

[0018] The aluminum-coated sheet and strip of the present invention have a yield strength ≥350MPa, a tensile strength ≥420MPa, and an elongation A50 ≥18%.

[0019] The aluminum-coated sheet and strip of the present invention are steel-aluminum, aluminum-steel-aluminum, or steel-aluminum-steel structures.

[0020] In the design of the chemical composition of the steel strip of the aluminum-coated sheet and strip of this invention:

[0021] Carbon (C) strengthens yield strength through solid solution and phase transformation, while simultaneously inhibiting the diffusion of Al in steel and the formation of iron-aluminum compounds. Excessive C content is detrimental to the subsequent processing properties of the material, such as stamping and deep drawing; however, higher C content tends to agglomerate at dislocation and other defect sites, negatively impacting surface quality. Based on actual steelmaking processes, this invention controls the C content to be between 0.04% and 0.09%.

[0022] Si is a deoxidizing element and a solid solution strengthening element, which increases yield strength and decreases elongation. Although an appropriate amount of Si is beneficial to improving the bonding performance of the steel-aluminum interface, it will also weaken the inhibitory effect of O (oxygen) on the formation of brittle compound layer at the steel-aluminum interface. Therefore, this invention controls 0 < Si ≤ 0.005%.

[0023] Mn is also a common strengthening element in steel. It increases yield strength through solid solution strengthening, but reduces elongation. Appropriate amounts of Mn can combine with sulfur in steel to form MnS, reducing the steel's hot brittleness. However, excessive Mn solid solution strengthens the microstructure, inhibits grain growth, and reduces γ-texture (ND∥). <111> The high strength of the material is very detrimental to the stamping and forming of steel plates and will also increase costs. Therefore, this invention controls its content to be between 0.40% and 0.80%.

[0024] In steel, phosphorus (P) is generally controlled as an impurity element, with its addition permitted only in a few special-purpose steels. For example, in sulfur-containing free-machining steels, adding no more than 0.15% P allows it to dissolve in ferrite, causing strengthening and embrittlement to improve its machinability. Additionally, P is a major corrosion-resistant element in traditional atmospheric corrosion-resistant steels; P in steel can accelerate the uniform dissolution of Fe. 2+ The oxidation rate helps to form a uniform FeOOH rust layer on the steel surface and promotes the formation of amorphous iron hydroxide FeO. x (OH) 3-2x A dense protective film effectively improves the atmospheric corrosion resistance of steel. Generally, the optimal corrosion resistance is achieved when the phosphorus (P) content is between 0.08% and 0.15%, so early atmospheric corrosion resistant steels used P as a corrosion-resistant element. However, excessive P causes "cold brittleness" in steel, reducing plasticity and impact toughness, and worsening weldability and cold bending performance. Therefore, the amount of P added is strictly limited for steels requiring low-temperature impact toughness or high formability. In recent years, some atmospheric corrosion resistant steels have also reduced the P content and chosen other alternative corrosion-resistant elements to ensure corrosion resistance, even controlling it as an impurity element with a content ≤0.015%. However, controlling the P content at such a low level increases the difficulty of steelmaking and raises manufacturing costs. This invention considers that P can improve the strength of steel for aluminum-clad laminates and strips through solid solution strengthening and phase transformation strengthening, while also improving the steel-aluminum bonding performance. Therefore, this invention adds 0.008% to 0.020% P.

[0025] Sulfur (S) is detrimental to the properties of steel, easily causing "hot brittleness," reducing the low-temperature toughness of steel, and worsening the bonding performance at the steel-aluminum interface. The addition of manganese (Mn) can form MnS with S, and increasing the Mn / S ratio can improve thermal ductility. It is necessary to control its content at the lowest possible level. Considering that excessively low content increases the difficulty of steelmaking and production costs, this invention requires that the S content be controlled below 0.008%.

[0026] Al is an important deoxidizing element in steel, but high levels of Al can easily diffuse to the steel-aluminum interface, worsening the interfacial bond strength. Therefore, its content must be controlled within a certain range; hence, this invention controls 0 < Al ≤ 0.005%.

[0027] Boron (B) is an extremely reactive element in steel, readily forming compounds with carbon (C) and nitrogen (N). Simultaneously, B readily segregates at austenite grain boundaries and dislocations, thus suppressing the segregation of other interstitial atoms at these locations. Furthermore, B segregation does not hinder dislocation movement, resulting in uniform strain, improved material plasticity, and beneficial effects on aluminum-coated rolling performance. B significantly improves hardenability; even trace amounts of B can effectively increase the strength of steel. However, excessively high B content can promote increased hardenability, leading to excessively high strength and reduced stamping performance. Therefore, this invention controls its content to 0.0005–0.002%.

[0028] N can form AlN particles with Al in steel, thereby binding Al and limiting its diffusion in steel. At the same time, similar to C, N tends to agglomerate at dislocations to form Cotillard atmospheres, which leads to strain concentration and causes uneven strain in aluminum-clad materials during processing, affecting surface quality. Moreover, excessive N also deteriorates impact toughness. Therefore, this invention controls its content to be 0.012-0.030%.

[0029] Oxygen (O) can suppress the adverse effects of Al in steel on the properties of aluminum cladding, so an appropriate amount of O is required. However, excessive oxygen can cause defects such as subcutaneous bubbles and porosity, and exacerbate the hot brittleness of sulfur, making the strip surface prone to defects such as peeling and slag inclusions. During the solidification process of steel, oxygen will precipitate in large quantities in the form of oxides, reducing the plasticity and impact toughness of the steel. Therefore, the O content should be controlled to be ≤0.01%.

[0030] In addition to the elements mentioned above, this invention also requires the selective addition of one or more of the following: Ti: 0.01–0.06%, Nb: 0.01–0.03%, Cu: 0.01–0.15%, Cr: 0.03–0.60%, and Ca: 0.001–0.004%, thereby further improving room temperature strength.

[0031] In steel, Cr forms a continuous solid solution with Fe, resulting in solid solution strengthening. It also forms various types of carbides with C, such as M3C, M7C3, and M... 23C6 and other elements produce a secondary strengthening effect. Simultaneously, the addition of Cr helps suppress Al diffusion and improves the bonding performance between steel and aluminum. Higher Cr content is detrimental to toughness, increases welding difficulty, and, as Cr is a valuable alloying element, its content is controlled at 0.03–0.6% in this invention.

[0032] Cu has solid solution and precipitation strengthening effects. At higher content, it exhibits a secondary hardening effect during tempering at appropriate temperatures, thereby increasing strength. Simultaneously, the addition of Cu also improves the bonding properties between steel and aluminum. Excessive Cu content causes cracks in the steel billet during heating and hot rolling, deteriorating surface properties. Therefore, this invention controls the Cu content to be between 0.01% and 0.15%.

[0033] Nitrogen (Nb) is a strong nitride-carbide-forming element. During post-rolling cooling, it can combine with carbon and nitrogen in steel to form intermediate phases such as NbC, Nb(CN), and NbN. The resulting fine carbide particles refine the microstructure, producing fine-grain strengthening and precipitation strengthening effects, significantly improving the strength of the steel. Furthermore, Nb can inhibit the expansion of austenite interfaces and increase the recrystallization temperature of steel, allowing for rolling in the non-recrystallization zone at higher temperatures. Therefore, adding an appropriate amount of Nb to steel is beneficial for strength improvement, but the effect no longer increases strength beyond 0.06%. Higher Nb content leads to the formation of coarse carbonitride particles at grain boundaries, deteriorating impact toughness. Therefore, Nb can be selectively added, but its content should be controlled between 0.01% and 0.03%.

[0034] Ti has high chemical reactivity, readily forming compounds with C, N, O, S, etc., and precipitating during rolling and cooling to increase strength. Simultaneously, the fine precipitates can pin grain boundaries, thereby refining austenite grains and preventing grain growth in the weld heat-affected zone, improving the weldability of the steel. The combined addition of Ti and B can significantly reduce temper brittleness. However, when the Ti content is too high, titanium nitride particles tend to grow and agglomerate at high temperatures, impairing the steel's plasticity and toughness. Therefore, its content needs to be controlled between 0.01% and 0.06%.

[0035] Adding Ca to steel can alter the shape of sulfides, suppress the hot brittleness of S, and improve toughness. However, the effect is not significant if the Ca content is too low, and when the content exceeds 0.005%, the resulting Ca(O,S) ions are too large, increasing brittleness and potentially becoming crack initiation points. Simultaneously, it reduces the purity of the steel and worsens the toughness of the weld heat-affected zone. Therefore, this invention limits its content to 0.001–0.004%.

[0036] The steel strip used for aluminum-clad sheets and strips involved in this invention is mainly for structural components that require resistance to atmospheric corrosion, such as containers and corrosion-resistant pipelines. Therefore, there are clear requirements for strength. On the one hand, the yield strength of the steel strip must be controlled to be ≥300MPa; on the other hand, the steel strip must have good plasticity to meet the requirements of aluminum-clad rolling, and it must also have good steel-aluminum bonding performance to ensure that the obtained aluminum-clad material does not delaminate during use.

[0037] To meet the aforementioned performance requirements, this invention rigorously designs the composition based on the influence of different alloying elements on these properties, achieving the performance requirements through the combined effect of multiple elements. The addition of carbon (C) provides both solid solution strengthening and phase transformation strengthening. Existing aluminum-coated steel patents (such as Chinese patent CN114250411A) generally control C ≤ 0.005% to ensure plasticity, which significantly increases the difficulty of steelmaking. This invention, to ensure the high strength of the aluminum-coated material while requiring a yield strength of over 300 MPa for the steel strip, uses 0.04–0.09% C. This serves two purposes: firstly, it provides solid solution strengthening; secondly, during steel production, controlled rolling and post-rolling cooling form a ferrite + small amount of bainite microstructure in the steel, resulting in phase transformation strengthening and increased strength.

[0038] Because aluminum-clad laminates undergo annealing heat treatment during production, conventional grain refinement strengthening methods are not very effective after heat treatment. However, solid solution strengthening is not limited by heat treatment. Therefore, the higher the strength of the steel used in the substrate, the higher the strength of the finished aluminum-clad laminate. To address this, this invention adds 0.4–0.8% Mn to ensure the strength of the steel used in the substrate through solid solution strengthening of Mn.

[0039] In this invention, the phosphorus (P) content is controlled at 0.008–0.020%. P is typically controlled as an impurity element in steel, so a lower content is desirable, generally below 0.015% or even lower. However, lower P content increases steelmaking costs and difficulty. Since P belongs to the same group as nitrogen (N), appropriate P content is beneficial to steel-aluminum bonding performance. However, research in this invention has found that its effect on improving steel-aluminum bonding performance is not linear; P content exceeding 0.020% begins to deteriorate steel-aluminum bonding performance. Therefore, considering the difficulty, cost, and performance requirements of steelmaking, the upper limit for P control is relaxed to 0.020%. This ensures steel-aluminum bonding performance while simultaneously improving strength and reducing steelmaking costs.

[0040] In the steel of this invention, Cr not only provides solid solution strengthening but also has a secondary strengthening effect. Cu also provides solid solution strengthening and can precipitate during heat treatment to enhance strength. Nb, V, and Ti precipitate fine carbonitrides during rolling and cooling, providing precipitation strengthening to the matrix.

[0041] Based on the strengthening effect of the above elements on steel, it is required to control the content of C, P, N and Mn in steel to meet the relationship 1: 150(C-0.01)+60P+300N+5Mn≥13.0. If the value of the relationship is lower than 13.0, the strength is likely to be low.

[0042] The key to improving the bonding performance of steel and aluminum lies in controlling the formation of brittle iron-aluminum compounds at the steel-aluminum interface in the aluminum-clad material. The formation of these compounds is closely related to the diffusion of Al in the steel; controlling Al diffusion can inhibit the formation of these compounds within a certain temperature range. This invention demonstrates that the synergistic effect of multiple elements such as C, Cu, O, and N can further improve the bonding performance of steel and aluminum. O (oxygen) and N can inhibit Al diffusion and reduce the formation of brittle iron-aluminum compounds, thereby improving the bonding performance. However, excessive O content will lead to subcutaneous bubbles and porosity in the cast billet, and exacerbate the hot brittleness caused by sulfur, making the steel surface prone to defects such as peeling and slag inclusions. Therefore, this invention limits the O content to ≤0.01%, while using 0.012–0.03% N to ensure the bonding performance of steel and aluminum. Si and Al, as deoxidizing elements, hinder the improvement effect of O on the bonding performance of steel and aluminum, so their content should be limited.

[0043] Therefore, this invention achieves excellent steel-aluminum bonding performance through the synergistic effect of multiple elements such as C, Mn, Si, Al, O, and N. Based on the relative strengths of the effects of C, N, O, Al, and Si on the steel-aluminum bonding performance, their contents are required to satisfy the relationship 2: 0.5C + 3.83N + O - 0.89Al - 1.15Si ≥ 0.08, thus ensuring excellent steel-aluminum bonding performance. A higher value in Equation 2 indicates better aluminum coating performance. Research in this application shows that if the value of the relationship is lower than 0.08, steel-aluminum delamination is prone to occur during processing and use.

[0044] Overall, this invention adopts the composition system required above, comprehensively considering the steel-aluminum bonding performance and high strength requirements. Through the combined effect of each element, it is possible to obtain steel for aluminum-clad sheets and strips that meets the requirements.

[0045] The method for producing high-strength aluminum-clad steel strip for corrosion-resistant structures according to the present invention includes the following steps:

[0046] 1) Cleaning and polishing of the surfaces of aluminum strip and steel strip composite;

[0047] 2) Rolling

[0048] Aluminum strip and steel strip are laminated and rolled at room temperature to form aluminum-coated sheet and strip, with a single-pass rolling deformation of 50-85%.

[0049] 3) Annealing

[0050] The coil is annealed in a bell-type furnace. The annealing temperature is 480-530℃, the annealing holding time is t = 120 + 3H, where t is in min and H is the thickness of the aluminum-coated steel coil in cm. After annealing, the coil is water-cooled to below 200℃ and then cooled in the furnace to below 80℃ before being removed from the furnace.

[0051] or,

[0052] Continuous annealing and winding; wherein, the annealing temperature is 480~530℃, the continuous annealing time t0=(h+1)×1.5±1min, h is the thickness of the aluminum-clad sheet / strip in mm, h≥1mm; h<1mm, annealing time≥2min;

[0053] 4) Finishing.

[0054] Preferably, in step 1), the surface cleaning includes pickling, degreasing, and drying.

[0055] Preferably, in step 1), the surface cleaning includes sandblasting or shot blasting.

[0056] Preferably, in step 1), the grinding is performed using a sanding belt or a grinding wheel, and the grinding direction is parallel to the rolling direction.

[0057] Preferably, in step 2), the rolling is a single-pass rolling or a two-pass rolling.

[0058] In the production process of the aluminum-coated sheet and strip described in this invention:

[0059] Surface cleaning of aluminum and steel strips includes necessary pickling, degreasing and drying, or direct sandblasting and shot blasting to remove oil, rust and oxide scale from the surface of the aluminum and steel strips.

[0060] Grinding is used to increase the roughness of the surfaces to be laminated and expose fresh base metal, thereby improving the mechanical bonding strength between steel and aluminum during the cladding rolling process. Grinding is preferably performed using abrasive belts or grinding wheels, which creates a rough surface, improving the mechanical interlocking of aluminum and steel during cladding rolling and resulting in better steel-aluminum bonding strength. Furthermore, grinding creates a microscopic work-hardened layer on the surfaces to be laminated. This hardened layer is broken up during the cladding rolling process, exposing fresh metal matrix and achieving point contact bonding between steel and aluminum, further enhancing the steel-aluminum bonding strength.

[0061] When rolling steel and aluminum at room temperature, the deformation per single pass should be controlled within the range of 50% to 85%. Depending on the requirements, steel and aluminum strips of different specifications are rolled into aluminum-clad sheets and strips of the desired thickness and structure in 1-2 passes. Lower deformation results in more rolling passes, requiring repeated feeding and threading, extending production time, reducing efficiency, and increasing costs. Furthermore, insufficient interfacial bonding strength due to excessively low deformation can lead to direct delamination of the steel and aluminum. While excessive deformation per pass increases rolling efficiency, it also results in high rolling loads and demanding equipment requirements. The choice between 1 or 2 passes depends on equipment capacity and finished product specifications.

[0062] After aluminum-coated rolling, the strip needs to be annealed. The purpose of annealing is twofold: firstly, to eliminate the work hardening generated during room temperature rolling and restore the plasticity of the aluminum-coated material, facilitating subsequent product forming and processing; secondly, to allow the atoms at the steel-aluminum interface to diffuse into each other during annealing, transitioning from a mechanical bond during rolling to a metallurgical bond, further improving the interfacial bonding strength.

[0063] Since aluminum has a melting point of approximately 640℃ (which may vary depending on the content of other alloys in the aluminum), and a corresponding recrystallization temperature of about 250℃, the annealing temperature is generally controlled to be at least 100-200℃ above the recrystallization temperature. Lower annealing temperatures will significantly increase annealing time, reduce production efficiency, and increase production costs. Conversely, excessively high annealing temperatures will increase energy consumption and production costs. Furthermore, higher temperatures provide the impetus for the formation of brittle phases at the steel-aluminum interface, reducing the interfacial bonding strength. Therefore, this invention controls the annealing temperature to be between 480 and 530℃, specifically determined based on the dimensions and specifications of the aluminum-clad sheet / strip and the performance of the finished product.

[0064] There are generally two annealing methods: conventional bell-type furnace annealing and continuous annealing. The annealing holding time t for aluminum-clad sheets and strips is determined comprehensively based on the thickness h (mm) of the aluminum-clad sheets and strips, the furnace temperature T (°C), and the annealing method.

[0065] When continuous annealing is used, the annealing time t0 = (h+1)×1.5±1min, where h≥1mm. If h<1mm, the annealing time shall not be less than 2min.

[0066] When using a bell-type furnace for annealing, the annealing time includes three stages: heating, holding, and cooling. The annealing time is closely related to the thickness of the aluminized sheet / strip, and for aluminized steel coils, it corresponds to the difference between the inner and outer radii of the coil. Generally, this is a linear relationship, but the specific ratio may vary depending on the actual situation. The annealing time t (min) during the holding stage is controlled based on the thickness H of the aluminized steel coil (the difference between its inner and outer radii), requiring the following condition: t = 120 + 3H, where H is in cm. Based on the bell-type furnace's inner diameter, the outer diameter of the aluminized coil is generally below 1800 mm, and the inner diameter is approximately 560 mm. Therefore, the holding time for the aluminized steel coil in the bell-type furnace should not exceed 306 min, approximately 5 hours. In existing technologies, when annealing aluminized coils in a bell-type furnace, the holding time is set based on the operator's experience, typically ranging from 15 to 18 hours. Additionally, heating requires 6 to 8 hours, and cooling requires approximately 6 hours.

[0067] This invention clarifies the linear relationship between annealing holding time and steel coil specifications, making it more operable. Compared with existing processes, the annealing process of this invention significantly shortens heat treatment time, reduces energy consumption, improves production efficiency, and lowers production costs.

[0068] Annealed aluminum-clad coils need to be finished, partly to improve the shape and trim the edges, and partly to further improve the surface quality through micro-pressure.

[0069] Because aluminum possesses corrosion resistance and aesthetic appeal, the aluminum-coated steel strips described in this invention can be used to manufacture corrosion-resistant components such as containers, corrosion-resistant pipes, and outdoor towers without the need for painting. In contrast, containers made of conventional weathering steel require sandblasting and the application of primer, intermediate coat, and topcoat; the cost of painting the container surface is estimated to exceed 1000 yuan per ton. Therefore, using the high-strength aluminum-coated steel strips described in this invention to manufacture high-strength corrosion-resistant components reduces surface painting compared to traditional weathering steel, significantly lowering production costs and improving production efficiency.

[0070] The present invention has the following advantages:

[0071] 1. This invention improves the strength of steel by using solid solution strengthening and phase transformation strengthening. In terms of composition design, it adopts a simple C-Mn design and controls the contents of C, P, N and Mn to satisfy the relationship: 150(C-0.01).

[0072] With +60P+300N+5Mn≥13.0, higher strength is achieved. Its yield strength is ≥300MPa and tensile strength is ≥360MPa, resulting in an aluminum-clad sheet / strip with a yield strength ≥330MPa and a tensile strength ≥420MPa. Primarily used in the production of aluminum-clad sheets / strips for containers and other structures requiring corrosion resistance, it offers superior corrosion resistance and a longer service life compared to existing weathering steels. Furthermore, it possesses the excellent appearance of aluminum, eliminating the need for painting and reducing coating costs, leading to lower overall costs.

[0073] 2. To achieve high steel-aluminum bonding performance, this invention requires that the contents of C, Mn, Si, Al, O, and N satisfy the following relationship in the composition design:

[0074] 0.5C+3.83N+O-0.89Al-1.15Si≥0.08, inhibits the formation of brittle iron-aluminum compounds at the steel-aluminum interface, thereby ensuring good steel-aluminum bonding performance of the steel plate and preventing steel-aluminum delamination during use.

[0075] 3. This invention adopts a low-oxygen, high-nitrogen composition design, limiting the O content to ≤0.01%, and using 0.012-0.03% N to compensate for the steel-aluminum bonding performance, thereby solving the defects such as subcutaneous bubbles and porosity in high-oxygen cast billets, reducing the occurrence of defects such as peeling and slag inclusions on the steel strip surface, and further improving the steel-aluminum bonding performance and surface quality of aluminum-coated sheets and strips.

[0076] 4. By controlling the P content to 0.008-0.020%, this invention utilizes the solid solution strengthening effect of P and its influence on the steel-aluminum bonding performance to further improve the steel-aluminum bonding performance. The aluminum-coated strip still has high steel-aluminum bonding performance after high-temperature nitriding treatment, while reducing the difficulty and cost of steelmaking and increasing production efficiency.

[0077] 5. This invention can employ either bell-type annealing or continuous annealing during the annealing stage, and establishes a linear relationship between annealing holding time and steel coil specifications. The annealing time is significantly shortened compared to the traditional bell-type annealing process, reducing energy consumption, improving production efficiency, lowering production costs, and enhancing operability. Attached Figure Description

[0078] Figure 1 This is a schematic diagram of the aluminum-coated sheet and strip of the present invention.

[0079] Figure 2 This is a schematic diagram of the aluminum-coated sheet and strip of the present invention.

[0080] Figure 3 This is a schematic diagram of the aluminum-coated sheet and strip of the present invention. Detailed Implementation

[0081] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0082] See Figure 1 , Figure 2 and Figure 3 The diagram shown is a structural schematic of an embodiment of the aluminum-coated strip of the present invention, wherein 1 is a steel strip and 2 is an aluminum strip.

[0083] According to the chemical composition requirements of steel strips for aluminum-clad sheets and strips involved in this invention, steel strips 1 and aluminum strips 2 of different specifications are selected, and after surface cleaning and grinding, aluminum-clad sheets and strips are obtained by aluminum-clad rolling and annealing. The finished aluminum-clad sheets and strips have a thickness of 0.5 to 2.0 mm.

[0084] The chemical composition of the steel strip in this embodiment of the invention is shown in Table 1, the specific production process parameters are shown in Table 2, and the performance of the finished product is shown in Table 3.

[0085] The aluminum-clad sheet and strip prepared using the components and process described in this invention have a yield strength ≥350MPa, tensile strength ≥420MPa, elongation A50 ≥18%, good plasticity, and excellent steel-aluminum interface bonding performance (no iron-aluminum compounds are formed).

[0086] Although the steel strips used in Comparative Examples 1-4 also employed a lower Si-Al design and added certain amounts of O and N, their overall composition differed from that of the present invention. The resulting performance also differed significantly from that of the present invention, as detailed in Table 3.

[0087] In Comparative Examples 1-4, the values ​​of Formula 1 and Formula 2 are both lower than those in the embodiments of the present invention. They were then subjected to aluminum-coated rolling and appropriate heat treatment according to the same process.

[0088] As can be seen from the results in Table 3, the strength of Comparative Examples 1-4 is significantly lower than that of the present invention and does not meet the requirements of the present invention. Considering that the aluminum-coated strip described in the present invention involves a lot of welding during the processing of high-strength corrosion-resistant structural parts, the requirements for the steel-aluminum bonding performance are higher. Therefore, the steel-aluminum bonding performance was tested under annealing heat treatment conditions higher than those for conventional aluminum-coated materials.

[0089] The obtained aluminized sheet and strip were heat-treated at 580℃ for 5 hours, and their aluminizing performance was tested and compared with that of the comparative example. As can be seen from Table 3, the comparative example's aluminized sheet and strip showed a small amount of iron-aluminum compounds at the steel-aluminum interface under the 580℃, 5-hour heat treatment conditions, while the aluminized sheet and strip of the present invention maintained a clean interface without the formation of iron-aluminum compounds, indicating that the aluminized sheet and strip obtained by the present invention has better steel-aluminum bonding performance.

[0090] The process of this invention can produce wide, high-strength aluminum-coated sheets and strips of various specifications as needed, for use in the production of container panels and other components requiring high strength and corrosion resistance. The sheets and strips have a good appearance, achieving a paint-free application effect, reducing painting processes and costs, resulting in lower overall costs. Furthermore, the heat treatment temperature can be adjusted as needed to obtain higher strength or better plasticity for use in the manufacture of other structural components requiring corrosion resistance and aesthetics.

[0091]

[0092]

[0093]

Claims

1. A high-strength aluminum-clad strip for corrosion-resistant structures, which is clad with a steel strip and an aluminum strip, the steel strip having a chemical composition by weight percent of C: 0.04-0.09%, 0 150 (C-0.01) + 60P + 300N + 5Mn ≥ 13.

0.

2. The high-strength aluminum-clad strip for corrosion-resistant structures according to claim 1, wherein the aluminum-clad strip is a clad strip in which the aluminum alloy layer is formed on one side of the steel sheet. The balance is Fe and other unavoidable impurities.

3. The high-strength aluminum-clad strip for corrosion-resistant structures according to claim 1 or 2, wherein the aluminum-clad strip is a clad strip in which the core material is a steel sheet, and the clad layer is an aluminum alloy layer. The steel strip has a yield strength of ≥ 300 MPa, a tensile strength of ≥ 360 MPa, and an elongation of ≥ 30%.

4. The high-strength aluminum-clad strip for corrosion-resistant structures according to claim 1 or 2, wherein the aluminum-clad strip is a clad strip in which the core material is a steel sheet, and the clad layer is an aluminum alloy layer. The aluminum-clad strip has a yield strength of ≥ 350 MPa, a tensile strength of ≥ 420 MPa, and an elongation A50 of ≥ 18%.

5. The high-strength aluminum-clad strip for corrosion-resistant structures according to claim 3, wherein the aluminum-clad strip is a clad strip in which the aluminum alloy layer is formed on one side of the steel sheet. The aluminum-clad strip has a yield strength of ≥ 350 MPa, a tensile strength of ≥ 420 MPa, and an elongation A50 of ≥ 18%.

6. The high-strength aluminum-clad strip for corrosion-resistant structures according to claim 1 or 2 or 5, wherein the aluminum-clad strip is a clad strip in which the core material is a steel sheet, and the clad layer is an aluminum alloy layer. The aluminum-clad strip is a steel-aluminum, aluminum-steel-aluminum, or steel-aluminum-steel structure.

7. The high-strength aluminum-clad strip for corrosion-resistant structures according to claim 3, wherein the aluminum-clad strip is a clad strip in which the aluminum alloy layer is formed on one side of the steel sheet. The aluminum-clad strip is a steel-aluminum, aluminum-steel-aluminum, or steel-aluminum-steel structure.

8. The high-strength aluminum-clad strip for corrosion-resistant structures according to claim 4, wherein the aluminum-clad strip is a clad strip in which the aluminum alloy layer is formed on one side of the steel sheet. The aluminum-clad strip is a steel-aluminum, aluminum-steel-aluminum, or steel-aluminum-steel structure.

9. The method of producing a high-strength aluminum-clad strip for corrosion-resistant structures according to any one of claims 1 to 8, characterized by, The method comprises the following steps: 1) cleaning and polishing the surfaces of the aluminum strip and the steel strip; 2) rolling The aluminum strip and the steel strip are rolled at room temperature to form the aluminum-clad strip, with a single-pass rolling deformation of 50-85%; 3) annealing coiling and batch furnace annealing; wherein the annealing temperature is 480-530°C, the annealing holding time t = 120 + 3H, t is in units of min, and H is the thickness of the aluminum-clad steel coil, in units of cm; after the annealing is completed, water cooling is performed to below 200°C, and finally furnace cooling is performed to below 80°C before the coil is discharged; or, continuous annealing and coiling; wherein the annealing temperature is 480-530°C, the continuous annealing time t0= (h + 1) x 1.5 ± 1 min, h is the thickness of the aluminum-clad strip, in units of mm, h ≥ 1 mm; when h < 1 mm, the annealing time is ≥ 2 min; 4) finishing.

10. The production method according to claim 9, wherein In step 1), the surface cleaning comprises pickling, degreasing, and drying.

11. The production method according to claim 9, wherein In step 1), the surface cleaning comprises sandblasting and shot blasting.

12. The production method according to claim 9, wherein In step 1), the polishing uses a sand belt or a grinding wheel, and the polishing direction is parallel to the rolling direction.

13. The production method according to claim 9, wherein In step 2), the rolling is single-pass rolling or two-pass rolling.

Images