A corrosion-resistant rolled composite steel plate and its manufacturing method

Abstract

A corrosion-resistant rolled composite steel plate and its manufacturing method are disclosed, comprising a substrate, a cladding layer, and a transition layer between the substrate and the cladding layer; the substrate has the following composition by weight percentage: C 0.01-0.10%, Si 0.2-0.7%, Mn 0.30-1.70%, Ti 0.006-0.012%, Als 0.008-0.018%, Nb 0.0090-0.050%, B 0.0010-0.0050%, N 0.0015-0.0050%, P≤0.017%, S≤0.020%, O≤0.0050%, with the balance including Fe and other unavoidable impurities; the cladding layer is stainless steel. This invention reduces the possibility of intergranular corrosion and failure of the stainless steel on the cladding side by blocking or reducing the diffusion of carbon elements at the interface of the composite steel plate. It comprehensively improves the corrosion resistance and safety performance of rolled composite steel plates under high-temperature conditions and is suitable for equipment in the power and chemical industries with working temperatures of room temperature to 300°C.

Description

Technical Field

[0001] This invention relates to corrosion-resistant steel and its manufacturing method, specifically to a corrosion-resistant rolled composite steel plate and its manufacturing method, which is suitable for equipment in the power and chemical industries with a working temperature range of room temperature to 300°C. Background Technology

[0002] Composite steel plates made of low-alloy steel and various corrosion-resistant materials are frequently used in crude oil processing, energy and chemical industries due to their high mechanical strength and strong corrosion resistance. With the rapid development of the national economy, the demand for raw materials related to various energy sources, such as petroleum and fertilizers, is increasing. To improve energy production efficiency, the increasing size, higher parameters (higher temperatures, higher pressures), and lightweighting of energy production and processing equipment are imperative. This equipment upgrade demand places higher requirements on the performance of steel plates used in manufacturing these equipment, requiring not only higher strength and hardness but also excellent toughness, processing and forming properties, and better corrosion resistance.

[0003] The traditional production process for composite steel plates is explosive bonding. The main problem with this process is that it generates a large amount of harmful gases, which has an adverse impact on the environment, meaning that this type of production process does not meet environmental protection requirements. At the same time, the bonding rate at the interface of the explosively bonded steel plates is low, sometimes failing to meet the requirement of a bonding rate of over 97%. When this type of steel plate is used to manufacture various high-temperature, high-pressure, and large-scale container equipment, it poses a significant safety hazard. Once the bonding joint of the composite steel plates detaches, the equipment will malfunction, which will have a huge impact on the safety of people's lives and property.

[0004] Compared to explosive bonding, rolled composite steel plates achieve a bonding rate of over 99%, and the production process is more environmentally friendly. Therefore, in recent years, the production scale and engineering applications of rolled composite steel plates have been expanding annually.

[0005] However, regardless of whether it's an explosively bonded steel plate or a rolled steel plate, a transition layer will form at the interface between the carbon steel and other corrosion-resistant materials. Especially when the steel plate is in long-term service at high temperatures, carbon elements in the carbon steel substrate can diffuse into the cladding stainless steel through the transition layer. Once a large number of carbides form in the cladding stainless steel, intergranular corrosion will occur, which will adversely affect the corrosion resistance of the cladding corrosion-resistant material, ultimately leading to the failure of the cladding material and creating a safety hazard.

[0006] Therefore, how to rationally design the alloy composition and production process of carbon steel base layer, and minimize the negative impact on the corrosion resistance of corrosion-resistant materials after carbon elements in carbon steel diffuse through the transition layer to the cladding stainless steel under long-term high-temperature service, has become an urgent requirement for improving the comprehensive performance and safety performance of rolled composite steel plates.

[0007] Existing technology, such as Chinese Patent Publication No. CN107310218A, discloses a composite bulletproof steel plate and its manufacturing method. This composite bulletproof steel plate includes alternating layers of hard steel and soft steel, wherein the surface layer of the composite bulletproof steel plate is a hard steel layer. The hard steel layer and the soft steel layer are atomically bonded through rolling. The chemical element mass percentages of the soft steel layer are: C: 0.001-0.01%, 0 < Si ≤ 0.005%, Mn: 0.05-0.15%, 0 < Al ≤ 0.005%, Ti: 0.01-0.10%, with the balance being Fe and other unavoidable impurities. The composite bulletproof steel plate has multiple layers of soft and hard steel. When subjected to projectile impact, the hard steel layer cracks into small fragments, consuming impact energy. Simultaneously, the soft steel layer alters the bullet's trajectory, increasing its resistance, thus providing better bulletproof performance. The core technical solution of this invention is to effectively dissipate the kinetic energy of a bullet by alternating layers of high-strength hard steel and low-toughness soft steel. However, the invention does not address the interface between the hard and soft steel layers, nor does it cover the diffusion of carbon from the carbon steel material into the composite material.

[0008] Chinese Patent Publication No. CN107310219A discloses "A bulletproof steel plate with excellent cold bending performance and its manufacturing method". This patent describes a bulletproof steel plate with excellent cold bending performance, comprising: three layers of soft steel and two layers of hard steel, wherein the three layers of soft steel and the two layers of hard steel are alternately arranged, and the surface layer of the bulletproof steel plate is a soft steel layer. The hard steel layer and the soft steel layer are atomically bonded through rolling composite processing. The chemical element mass percentages of the soft steel layer are: C: 0.001-0.01%, 0 < Si ≤ 0.005%, Mn: 0.05-0.15%, 0 < Al ≤ 0.005%, Ti: 0.01-0.10%, with the balance being Fe and other unavoidable impurities. The hard steel layer alters the projectile's trajectory, while the soft steel layer on the surface, with its excellent plasticity, prevents cracking during extension and deformation. Upon impact, it breaks into small fragments, dissipating the impact energy. Simultaneously, the soft steel layer in the core alters the bullet's trajectory, increasing drag and thus providing better ballistic protection. This patent utilizes a technique of alternating hard and soft steel layers to reduce the bullet's kinetic energy. The technical solution does not address the interface between the rolled composite steel plates or element diffusion.

[0009] Chinese Patent Publication No. CN108231273A discloses a method for improving the interface of copper-aluminum composite materials, comprising the following steps: pre-coating or depositing graphene at the copper-aluminum interface, and then processing and compositening copper, aluminum, and graphene; the coating or deposition method is one of coating, electroplating, or chemical vapor deposition; the processing and composite method is one of rolling composite, extrusion composite, or drawing composite; the graphene is powder or film. Using the method of this invention, adding graphene to the copper-aluminum interface can improve the interface bonding and conductivity while ensuring interfacial adhesion and preventing the formation of brittle and poorly conductive intermetallic compounds. This patent relates to a method for improving the interface position of composite materials; however, since the substrate and composite material are copper and aluminum respectively, it has limited relevance to the composite rolling technology of carbon steel and stainless steel. The patent also does not mention the influence of element diffusion at the interface on material properties.

[0010] In summary, existing rolled composite steel plate technologies offer little consideration for the transition layer at the interface between the base material and the cladding material, particularly regarding the impact of elements in the base material on the performance of the cladding stainless steel through this transition layer. Essentially, no specific measures have been taken to reduce the likelihood of weakened stainless steel corrosion resistance due to carbide precipitation at the composite material interface. Especially in the chemical and energy industries, composite steel plate manufacturing equipment often operates at high temperatures (below 300°C). If this equipment operates at high temperatures for decades, elements at the material interface may diffuse further. In particular, carbon from the carbon steel side diffuses into the stainless steel cladding, forming more carbides and further reducing the stainless steel's corrosion resistance, creating potential safety hazards. Summary of the Invention

[0011] The purpose of this invention is to provide a corrosion-resistant rolled composite steel plate and its manufacturing method. By blocking or reducing the diffusion of carbon elements on the carbon steel side at the interface of the composite steel plate, the possibility of failure due to intergranular corrosion of the stainless steel on the cladding side is reduced, thereby comprehensively improving the corrosion resistance and safety performance of the rolled composite steel plate under high-temperature working conditions. It is suitable for equipment in the power and chemical industries with working temperatures of room temperature to 300°C.

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

[0013] The composite steel plate substrate of the present invention forms a large number of finely dispersed and high-temperature stable MC (M represents one or more of Nb and Ti) precipitates. These stable carbide precipitates can fix the free carbon elements in the carbon steel substrate, thereby avoiding the diffusion and migration of carbon elements in the carbon steel to the interface of the rolled composite steel plate under high-temperature working conditions, which would lead to an increase in the carbon element concentration in the stainless steel near the interface, and generate a large number of carbide precipitates at the stainless steel grain boundaries, inducing intergranular corrosion, and ultimately weakening or even losing the anti-corrosion function of the composite material.

[0014] Specifically, the corrosion-resistant rolled composite steel plate of the present invention comprises a substrate, a cladding layer, and a transition layer between the substrate and the cladding layer; wherein, the substrate comprises the following components by weight percentage: C: 0.01%–0.10%, Si: 0.2%–0.7%, Mn: 0.30%–1.70%, Ti: 0.006%–0.012%, Als: 0.008%–0.018%, Nb: 0.0090%–0.050%, B: 0.0010%–0.0050%, N: 0.0015%–0.0050%, P≤0.017%, S≤0.020%, O≤0.0050%, with the balance including Fe and other unavoidable impurities;

[0015] The surface microstructure of the composite steel plate substrate consists of 60–80% ferrite + 20–40% pearlite + MC precipitates, while the central microstructure consists of 30–40% pearlite + 60–70% ferrite + MC precipitates. Here, M represents one or both of Nb and Ti, the average major axis length of the MC precipitates is less than 600 nm, and the bulk density of MC precipitates with a major axis length less than 600 nm is greater than 2.0 × 10⁻⁶. 4 pcs / mm 3 ;

[0016] The composite steel plate cladding is made of stainless steel, and its microstructure contains MC precipitates, where M represents one or more of Cr, Mo, Nb, and Ti. The average major axis length of the MC precipitates is less than 700 nm, and the bulk density of the MC precipitates is less than 1.0 × 10⁻⁶. 4 pcs / mm 3 Preferably, the stainless steel is austenitic stainless steel, ferritic stainless steel, duplex stainless steel, or super stainless steel.

[0017] Furthermore, the composite steel plate substrate composition contains Fe and other unavoidable impurities in the remainder.

[0018] Furthermore, the composite steel plate substrate also contains at least one of the following chemical elements: 0 < Ca ≤ 0.0055%, 0 < Ni ≤ 0.65%, and 0 < Cu ≤ 0.55%.

[0019] Preferably, in the composite steel plate substrate, the proportion of MC precipitates with a long axis length of less than 600 nm to the total number of MC precipitates is greater than 50%.

[0020] Preferably, in the composite steel plate cladding, the proportion of MC precipitates with a long axis length of less than 700 nm to the total number of MC precipitates is greater than 50%.

[0021] Furthermore, the microstructure of the composite steel plate cladding also contains a very small amount of σ phase, with the proportion of σ phase ≤ 1.5%, preferably, the proportion of σ phase near the transition layer ≤ 0.5%.

[0022] Preferably, the thickness of the composite steel plate substrate is ≥6mm, the thickness of the cladding layer is ≥2mm, and preferably, the thickness of the transition layer is ≤230μm.

[0023] The composite steel plate substrate of the present invention has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the shear strength of the composite steel plate is ≥280MPa.

[0024] In the design of the composite steel plate substrate composition described in this invention:

[0025] Carbon (C) is an important strengthening element. To ensure appropriate strength in carbon steel plates, the mass percentage of C in the steel needs to be controlled to be greater than or equal to 0.01%. Simultaneously, to improve the weldability of the base carbon steel material, the upper limit of C content in the carbon steel needs to be controlled. Furthermore, if the carbon content in the carbon steel base material is high, the difference in carbon concentration gradient between the two materials can lead to large-scale carbon migration at the interface between the base material and the stainless steel cladding material, causing intergranular corrosion in the stainless steel. Therefore, its upper limit is controlled at 0.10%. Accordingly, based on this, the present invention controls the C content to be between 0.01% and 0.10%.

[0026] Si (Si): Similar to carbon, silicon is a commonly used strengthening element in low-alloy steel. Adding a certain amount of Si to steel can improve its strength. Simultaneously, Si is a weak deoxidizer, playing an auxiliary role in deoxidation during the smelting process. Most of the SiO2 products formed after deoxidation are removed into the steel slag and do not affect the steel's properties. Furthermore, adding a certain amount of Si to steel can reduce the solubility of carbon in austenite, thereby promoting carbon desolvation, promoting the formation of MC precipitates, fixing carbon in the steel, and preventing large-scale carbon diffusion. Therefore, a certain amount of Si needs to be added to steel. However, excessive Si will reduce the weldability of steel. Because silicon has a stronger affinity for oxygen than iron, it easily forms low-melting-point silicates during welding, increasing the fluidity of slag and molten metal, causing spattering, and affecting the quality of the weld joint. Therefore, controlling the Si content within a certain range helps improve the weldability of steel. Therefore, this invention controls the Si content at 0.2% to 0.7%.

[0027] Mn: Mn is also an important strengthening element, which can effectively improve the strength of the base steel plate. At the same time, Mn is an effective austenite stabilizing element; adding a certain amount of Mn can increase the hardenability of steel. Therefore, to ensure the strength of the steel, the lower limit of Mn content is 0.30%. However, Mn is prone to causing center segregation in steel. Excessive addition of Mn will cause severe segregation at the center of the steel plate thickness, reducing the low-temperature toughness of the steel core. Therefore, the upper limit of Mn content is limited to 1.70%. Based on this, the present invention controls the Mn content between 0.30% and 1.7%.

[0028] Ti: Ti is both a deoxidizing element and a strong carbide-forming and nitride-forming element. In this invention, adding an appropriate amount of Ti can, on the one hand, form a stable MC precipitate in the steel, fixing the carbon element in the matrix and preventing its diffusion to the composite material interface. Simultaneously, some Ti participates in fixing free N elements in the steel, forming TiN precipitates. TiN precipitates can inhibit austenite grain growth, refine the grains, and thus simultaneously improve the strength and toughness of the steel plate. After Ti fixes some free nitrogen elements, it helps ensure that B elements exist in the steel in a free state, improving the hardenability of the steel. Furthermore, Ti deoxidizes and forms Ti2O3 particles, thereby promoting the formation of intragranular ferrite and improving the low-temperature impact toughness of the steel. However, when the Ti content in the steel is too high, the size of the formed TiN and Ti2O3 particles becomes larger, thus losing their ability to inhibit austenite growth and the formation of intragranular ferrite. Instead, they easily become sources of crack initiation, reducing the low-temperature impact toughness of the steel. Therefore, the upper limit for Ti is 0.012%. Based on this, the Ti content is controlled at 0.006% to 0.012% in this invention.

[0029] Als: Al is an important deoxidizing element that forms alumina inclusions. Furthermore, Al can combine with nitrogen (N) in steel to form AlN precipitates, reducing the content of free N in the steel. This prevents the combination of boron (B) and nitrogen, promoting the increase of free B content, improving hardenability, and contributing to the strength of the steel plate. However, when the acid-soluble aluminum content in the steel is too high, the size of the deoxidation product, alumina, increases. Due to the strong adsorption capacity between alumina inclusions, large alumina clusters form. These clusters can clog the nozzles during steelmaking, affecting the casting process. If these large clusters enter the steel plate, they will cause the steel plate to fail inclusion rating and flaw detection tests. Therefore, this invention controls the acid-soluble Al content to be between 0.008% and 0.018%.

[0030] Nitrogen (Nb): Nitrogen is a strong carbide-forming element. It can combine with carbon in steel to form molybdenum (MC) precipitates, stabilizing the carbon and preventing its diffusion to the interface. Adding an appropriate amount of Nb can also increase the recrystallization temperature of the steel. When the steel is recrystallized and rolled in the austenitic region, the austenitic grains will not grow rapidly, resulting in fine-grained steel with higher strength and toughness. However, if the Nb content in the steel is too high, the resulting MC precipitates will be larger, which will reduce the toughness of the steel plate and worsen the toughness of the weld heat-affected zone. Therefore, this invention controls the Nb content to be between 0.0090% and 0.050%.

[0031] B: Adding an appropriate amount of boron (B) is to compensate for the decrease in the strength of the steel plate caused by the reduction of dissolved carbon content after the carbon in the steel is fixed by stable carbides. If boron exists in the steel in a free state, some of it will preferentially occupy grain boundary sites, improving the hardenability of the steel plate. Therefore, the prerequisite for boron to function is that it must exist in the steel in a free state. Thus, to prevent boron in the steel from combining with oxygen and nitrogen to form boron oxide and boron nitride, the oxygen and nitrogen contents in the steel must be carefully controlled, which is a key point in alloy composition design. However, it should be noted that adding excessive boron to the steel can easily lead to excessive segregation at grain boundaries, which is detrimental to the toughness of the steel. Therefore, this invention controls the boron content to 0.0010% ≤ B ≤ 0.0050%.

[0032] Nitrogen (N): Appropriate amounts of Ti and Al elements are added. These two elements can form TiN and AlN precipitates with nitrogen in the steel. When these precipitates are fine and dispersed, they can refine the austenite grains, thereby improving the strength and toughness of the steel plate. However, when the nitrogen content in the steel is too high, the excess nitrogen will combine with boron (B) in the steel to form boron (BN), consuming free boron and reducing the influence of boron on improving the strength of the steel plate. At the same time, excessive nitrogen will have an adverse effect on the toughness of the steel, especially when the solid solution nitrogen content exceeds 0.005%, which will significantly reduce the low-temperature toughness of the steel plate. Therefore, this invention controls the nitrogen content to 0.0015 ≤ N ≤ 0.0050%.

[0033] Preferably, the composite steel plate substrate of the present invention further contains at least one of the following chemical elements: 0 < Ca ≤ 0.0055%, 0 < Ni ≤ 0.65%, and 0 < Cu ≤ 0.55%.

[0034] Ca: Ca is a strong deoxidizing element. Adding an appropriate amount of calcium can control the oxygen content in steel, thereby preventing the oxidation of boron. However, when the Ca content in steel exceeds 0.0055%, large inclusions of calcium oxide and calcium sulfide are easily formed, which is detrimental to the toughness of the steel. Therefore, this invention controls the Ca content to 0 < Ca ≤ 0.0055%.

[0035] Ni: Ni is a typical austenitic stabilizing element that can significantly improve the hardenability of steel plates, as well as their low-temperature toughness. However, Ni is relatively expensive, and considering the overall production cost of steel, excessive Ni should not be added to steel. Therefore, this invention controls the Ni content to 0 < Ni ≤ 0.65%.

[0036] Cu: Adding an appropriate amount of Cu helps to improve the strength of steel and enhance its corrosion resistance. However, when the Cu content in steel is too high, the steel plate is prone to high-temperature brittleness at high temperatures. Therefore, this invention controls the Cu content to 0 < Cu ≤ 0.55%.

[0037] It should be noted that the addition of the above-mentioned Ca, Ni and Cu elements will increase the production cost of the material. Taking into account both performance and cost control, in the technical solution described in this invention, at least one of the above-mentioned elements can be added preferably.

[0038] The composite steel plate substrate of this invention contains unavoidable impurities, P≤0.017%, S≤0.020%, O≤0.0050%.

[0039] P, S, and O are all impurity elements in steel. When technical conditions permit, the content of impurity elements in steel should be reduced as much as possible in order to obtain steel with better performance and higher quality.

[0040] P: For most steel plates, phosphorus (P) is considered a harmful element. The main reason is that P readily segregates towards grain boundaries, reducing the bonding force between atoms at these boundaries and causing temper embrittlement of the steel plate. This is especially true when the steel plate is subjected to high temperatures, which further exacerbates the temper embrittlement effect of P. Therefore, this invention controls the P content to ≤0.017%.

[0041] Sulfur (S): Sulfur (S) in steel readily combines with manganese (Mn) to form MnS inclusions. The higher the S content, the larger the MnS inclusions, which negatively impacts the strength and toughness of the steel plate. Furthermore, excessively high S content can lead to center segregation in the slab and increase the likelihood of hot cracking. Therefore, this invention controls the S content to ≤0.020%.

[0042] O: Oxygen in steel exists primarily in the form of oxides. When the O content in steel is too high, it indicates an excess of oxides, potentially leading to large inclusions and affecting the strength and toughness of the steel plate. Therefore, this invention controls the O content to ≤0.0050%.

[0043] The surface microstructure of the composite steel plate substrate described in this invention consists of 60-80% ferrite and 20-40% pearlite, while the central microstructure consists of 30-40% pearlite and 60-70% ferrite. Since this invention relates to composite steel plates operating at a maximum temperature of 300°C, controlling the microstructure of the composite steel plate substrate to be ferrite + pearlite satisfies the required strength and toughness properties for this operating condition. Controlling the pearlite content in the surface microstructure to 20-40%, slightly lower than the 30-40% in the central microstructure, aims to reduce the pearlite content in the surface microstructure while maintaining the basic mechanical properties of the material. This reduces the carbon concentration at the surface, thereby lowering the carbon concentration difference between the two sides of the transition layer and weakening the concentration barrier for carbon migration from the substrate surface to the transition layer.

[0044] In this invention, the rolled composite steel plate substrate contains stable MC precipitates, where M represents one or both of Nb and Ti, and the average major axis length of the MC precipitates is less than 600 nm. When the major axis length of the precipitates is large, they are prone to forming crack initiation sites for microcracks inside the steel plate, thus adversely affecting the mechanical properties of the steel plate. Therefore, it is necessary to control the average major axis length of MC in the substrate to be less than 600 nm. To ensure that the carbide precipitates form as small as possible in the substrate of the rolled composite steel plate of this invention, the carbide carbon fixation function is fully utilized without adversely affecting the mechanical properties of the steel plate due to carbide precipitation. Therefore, the proportion of MC precipitates with a major axis length less than 600 nm to the total number of MC precipitates is limited to greater than 50%.

[0045] The bulk density of the MC precipitate with a major axis dimension less than 600 nm in the substrate of the present invention is greater than 2.0 × 10⁻⁶.4 pcs / mm 3 In this invention, to prevent free carbon elements from diffusing into the cladding material in the base steel plate, a MC precipitate phase is formed in the steel to immobilize the free carbon elements through composition and process control. Therefore, in this invention, it is necessary to ensure that the bulk density of the MC precipitate phase with a major axis dimension less than 600 nm is greater than 2.0 × 10⁻⁶. 4 pcs / mm 3 Only in this way can the carbon element in the steel be effectively controlled, and the large-scale diffusion of free carbon elements to the stainless steel side be avoided.

[0046] The composite steel plate cladding material of this invention contains a stable MC precipitate phase, where M represents one or more of Cr, Mo, Nb, and Ti, and the average major axis length of the MC precipitate phase is less than 700 nm. The larger the carbide size in the cladding material, the greater the impact on the corrosion resistance of the stainless steel. Therefore, it is desirable for the carbide precipitate size in the cladding material to be as small as possible. However, during the production process of the cladding material and the rolled composite steel plate, some carbide precipitates are inevitably generated. To ensure the corrosion resistance of the rolled composite steel plate, this invention requires that the average major axis length of the MC precipitate phase in the cladding material be less than 700 nm.

[0047] The bulk density of the MC precipitate in the multilayer material of the present invention is less than 1.0 × 10⁻⁶. 4 pcs / mm 3 From the perspective of controlling the amount of carbide precipitates in composite materials, it is desirable to have as few carbides as possible, that is, to control their bulk density as low as possible. However, some carbides inevitably form during the heat treatment of composite steel plates. Controlling the bulk density of carbides to less than 1.0 × 10⁻⁶ is crucial. 4 pcs / mm 3 This ensures the excellent corrosion resistance of the multilayer material.

[0048] In the composite material described in this invention, the proportion of MC precipitates with a long axis length less than 700 nm to all MC precipitates is greater than 50%. In this invention, the "bulk density" of the MC precipitates is determined according to the method described in the YB / T 5320-2006 standard. To minimize the number of carbide precipitates in the composite material and thus increase its corrosion resistance, this invention limits the size and quantity of MC precipitates, specifically, the proportion of MC precipitates with a long axis length less than 700 nm to all MC precipitates is greater than 50%. When the number and size of the carbide precipitates exceed the limit, the corrosion resistance of the composite material will be significantly reduced, affecting the safe service performance of the rolled composite steel plate.

[0049] The cladding layer described in this invention is stainless steel (including austenitic stainless steel, ferritic stainless steel, duplex stainless steel, super stainless steel, etc.). The σ phase in its microstructure is a highly hard and low-ductility intermetallic phase. When present in stainless steel, especially when precipitated along grain boundaries, it significantly affects the steel's ductility, leading to a substantial reduction in impact toughness. Therefore, the σ phase proportion in stainless steel is ≤1.5%, especially near the bonding interface (transition layer) where the σ phase proportion is ≤0.5%.

[0050] The present invention also provides a method for manufacturing the corrosion-resistant rolled composite steel plate, which includes the following steps:

[0051] 1) Smelting and casting to obtain base material and multilayered billet.

[0052] The base material billet is obtained by smelting and casting according to the above composition; during the smelting process, deoxidizers Mn+Si, Al, and Ti alloy are added to the molten steel in sequence for deoxidation. During this process, Mn+Si and Al are added in sequence for pre-deoxidation. After pre-deoxidation, the oxygen content of the molten steel is 0.0020% to 0.0075%. Then Ti is added for final deoxidation. After deoxidation, element B is added. After casting, a carbon steel base material billet is obtained. At the same time, a stainless steel clad billet is also obtained.

[0053] 2) Billet assembly

[0054] After surface treatment of the base casting billet and the cladding billet, they are stacked together, the perimeter of the stacked casting billet is welded and sealed, vacuum is drawn, and then sealed again to form a composite slab; preferably, the vacuum degree after vacuuming is 8 to 60 Pa.

[0055] 3) Rolling of composite slabs

[0056] The composite slab is heated to 1020-1200℃ and then rolled in two stages. The total reduction rate of the composite slab in the first stage rolling is not less than 60%, the total reduction rate in the second stage rolling is not less than 20%, and the reduction rate in the last pass is 10-18%. The total reduction rate of the two stages rolling is not less than 80%, and the final rolling temperature is above 850℃.

[0057] 4) Heat treatment: Quenching and tempering are performed on the composite steel plate.

[0058] Preferably, in step 2), the surfaces of the substrate and the clad casting are surface treated to ensure that the surface of the casting is free of obvious oil stains, slag inclusions, cracks and other surface defects, and at the same time, the roughness of the surface of the casting is not greater than 2.0Ra.

[0059] Preferably, in step 4), the quenching temperature is 920~955℃, the quenching holding time is T1=(1~1.2)H, and after the holding time is completed, the plate is removed from the furnace and water-cooled to room temperature. Here, T1 is in min and H is the thickness of the steel plate in mm.

[0060] Preferably, in step 4), the tempering temperature is 550-700℃, and the tempering holding time is T2 = (1-1.5)H, where T2 is in min and H is the thickness of the steel plate in mm.

[0061] In the manufacturing method described in this invention

[0062] The composite steel plate substrate of this invention requires the generation of a large number of uniformly dispersed nanoscale MC precipitates. These MC precipitates fix the free carbon elements in the carbon steel substrate, preventing excessive diffusion of carbon elements to the substrate-composite interface, which could lead to the formation of carbides in the stainless steel and reduce its corrosion resistance. This improves the service safety performance of the rolled composite steel plate for high-temperature equipment. However, free carbon in steel is a major strengthening element in carbon steel substrates. When most of the free carbon elements are fixed in the form of MC, the strength of the carbon steel decreases. To compensate for the strength loss due to carbon fixation, boron (B) is added to improve the hardenability of the steel plate. The hardenability of boron mainly depends on the distribution of free boron at grain boundaries. Because boron is a highly reactive element, it can combine with oxygen in molten steel to form boron oxide; and it also readily combines with nitrogen (N) to form boron carbide.

[0063] Therefore, the deoxidation sequence of molten steel and the timing of the addition of element B are specifically designed in the technical solution of this invention. Specifically, during deoxidation, pre-deoxidation is first performed using Si + Mn, causing most of the silicon oxide and manganese oxide to float to the top slag. Using the strong deoxidizer Al, the oxygen level (determined according to the method for measuring oxygen content in molten steel as described in ISO 14284:1996) can be controlled relatively precisely between 0.0020% and 0.0075%. Then, final deoxidation is performed using Ti, forming a large amount of Ti oxides. Simultaneously, the added Ti can combine with free nitrogen elements in the steel to form TiN. The addition of Ti further reduces the free oxygen concentration in the steel. Within a certain oxygen content range (0.0020% to 0.0075%), the size of the Ti₂O₃ inclusions formed after deoxidation is suitable (2-5 μm), which is beneficial for the formation of some acicular ferrite structure during solidification and subsequent phase transformation, thus improving the toughness of the steel plate. In addition, Ti can also combine with N in the steel to form some TiN. On the one hand, this reduces the adverse effects of dissolved nitrogen on the toughness of the steel. On the other hand, TiN can precipitate at high temperatures during solidification, playing a role in pinning austenite growth and refining the original austenite grains. When the oxygen and titanium elements in the steel are properly controlled, adding an appropriate amount of B ensures that the added B mainly exists in a free state in the steel, ensuring that the base steel plate has high hardenability and significantly improving the strength of the steel plate.

[0064] In step 2), the surfaces of the base material and composite slab are processed to ensure that there are no obvious surface defects such as oil stains, slag inclusions, or cracks on the slab surface, and the surface roughness of the processed slab must not exceed 2.0 Ra. After vacuuming, the vacuum degree is 8-60 Pa, thus ensuring the rolling effect of the composite slab.

[0065] In step 3), the composite slab is heated to 1020 to 1200°C for rolling because: when the heating temperature is below 1020°C, the carbides and nitrides in the base slab cannot be completely dissolved, which reduces the pinning effect of the carbides on the austenite grains during rolling; at the same time, within this temperature range, it is beneficial to the homogenization of austenite in the cladding material, and the carbides in the cladding material are also completely dissolved. However, when the slab heating temperature is above 1200°C, it is easy to cause rapid growth of austenite grains in both the base material and the cladding material, which damages the mechanical properties of the steel.

[0066] Accordingly, it is preferred that the total reduction rate of the slab in the first stage of rolling is not less than 60%, the total reduction rate in the second stage of rolling is not less than 20%, the reduction rate in the last pass is 8-18%, the total cumulative reduction rate of the two stages of rolling is not less than 80%, and the final rolling temperature is above 850℃.

[0067] The first-stage high-temperature and high-reduction rolling process allows the material to fully recrystallize during the rolling deformation process, continuously refining the austenite grains. This inhibits the formation of larger austenite grains in the steel, thereby improving the low-temperature toughness of the steel. When the total reduction rate in the first stage is less than 60%, the austenite grain size in the steel is larger, which is not conducive to the strength and toughness of the steel plate.

[0068] The total reduction rate in the second stage of rolling should not be less than 20%, which can further promote austenite grain refinement. The reduction rate of the final rolling pass should be between 8% and 18%, which can increase the dislocation density in the steel and ensure the strength of the steel plate. If the reduction rate is less than 8%, the dislocation density is low, which is not conducive to strength improvement. If the reduction rate is higher than 18%, the rolling torque is too large, which is detrimental to the rolling equipment. If the final rolling temperature is lower than 850℃, the deformation resistance of the steel plate increases, making it difficult to guarantee a large final rolling reduction rate.

[0069] In step 4), the quenching temperature is 920~955℃, the quenching holding time is T1=(1~1.2)H, and after the holding time is completed, the plate is taken out of the furnace and water-cooled to room temperature. Here, T1 is in min and H is the thickness of the steel plate in mm.

[0070] It should be noted that during the quenching process, when the quenching temperature is below 920℃, the homogenization of austenite in the steel requires a longer time, which reduces heat treatment efficiency. Conversely, if the quenching temperature is above 955℃, some austenite in the carbon steel tends to grow, easily forming a mixed-grain structure, which is detrimental to the uniformity of the steel structure. Correspondingly, when the quenching holding time T1 is less than 1 hour, sufficient austenitization cannot be achieved, and when the quenching holding time T1 exceeds 1.2 hours, it exceeds the required austenitization time, reducing the efficiency of the quenching process.

[0071] In step 4), the tempering temperature is 550-700℃, and the tempering holding time is T2 = (1-1.5)H, where T2 is in min and H is the thickness of the steel plate in mm.

[0072] Step 4) During tempering, when the tempering temperature of the steel is below 550℃, a longer tempering time is required to remove residual quenching stress, which reduces tempering efficiency and slows down the formation rate of MC precipitates in carbon steel. Conversely, when the tempering temperature is above 700℃, the MC precipitates in the steel are prone to Ostwald coarsening and agglomeration, hindering the formation of fine, dispersed MC precipitates. Correspondingly, when the tempering holding time T2 is below 1.0H, the quenching stress in the steel tends not to be completely removed, while when the tempering holding time T2 is above 1.5H, the MC precipitates in the steel tend to coarsen, reducing the production efficiency of the tempering process.

[0073] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0074] 1. This invention utilizes finely dispersed spherical (2-5 μm) Ti₂O₃ oxides formed in steel as nucleation sites for MC carbide precipitates. Combined with optimized alloy composition and heat treatment processes, this allows for the formation of numerous dispersed nanoscale MC (M represents one or more of Nb and Ti) precipitates in the substrate. These precipitates fix free carbon elements in the substrate, reducing carbon diffusion and aggregation at the composite interface, thus decreasing the precipitation of stainless steel grain boundary carbides and ensuring the corrosion resistance of the composite rolled steel plate. Specifically, when this rolled composite steel plate is used in high-temperature equipment, even under conditions of 300°C, the high-melting-point Ti₂O₃ oxides (melting point 2130°C) formed during the controlled smelting process remain stably present in the steel, continuing to function as nucleation sites for MC carbides. Even free carbon elements present in steel can still react with alloying elements in steel using Ti2O3 oxide as a nucleation core to generate fine MC carbides, thereby further fixing carbon elements, ensuring that carbon elements in carbon steel do not diffuse to the interface, and protecting the corrosion resistance of rolled composite steel plates under long-term high-temperature service conditions.

[0075] 2. In the current production process of low-alloy high-strength steel, aluminum is commonly used as a deoxidizer to reduce the oxygen content in the steel as much as possible. The advantage of aluminum deoxidation is its high efficiency, but its disadvantage is that the Al2O3 inclusions formed in the molten steel after aluminum deoxidation can adversely affect the flaw detection and performance of the steel plate. This is mainly because individual Al2O3 inclusions are often irregular and sharp, easily forming crack initiation points within the material during stress. Simultaneously, Al2O3 inclusions readily aggregate and grow in molten steel, forming large Al2O3 inclusion clusters that can clog the casting nozzle. Furthermore, the presence of large inclusions in the steel can easily cause fluctuations in the tensile and impact properties of the steel plate. Additionally, Al2O3 inclusions cannot serve as nucleation sites for carbide precipitates.

[0076] In this invention, by controlling the type, sequence, and amount of deoxidizer added during the steelmaking process, finely dispersed spherical (2-5 μm) Ti2O3 oxides with high melting points are ultimately formed in the steel. Ti2O3 oxides do not easily aggregate and grow in molten steel, have no sharp edges, and do not significantly damage the flaw detection and mechanical properties of the steel plate, thus optimizing the microstructure. By controlling the element content ratio, TiN precipitation is controlled, refining the austenite grains. By designing the order of adding steel alloys, the oxidation and nitriding of boron can be effectively reduced, thereby maximizing the utilization of added boron, enhancing the hardenability of the steel plate, refining the grains, and ensuring the steel plate has high strength and excellent low-temperature toughness.

[0077] Furthermore, through smelting process control, especially by controlling the type, sequence, and amount of deoxidizer added, finely dispersed spherical (2-5 μm) Ti₂O₃ oxides formed in the steel can serve as nucleation sites for MC carbide precipitates. Combined with optimized alloy composition and heat treatment process design, a large number of dispersed nanoscale MC (M represents one or more of Nb and Ti) precipitates can be formed in the substrate. These precipitates can fix free carbon elements in the substrate, reduce the diffusion and aggregation of carbon elements at the composite interface, reduce the precipitation of stainless steel grain boundary carbides, and ensure the corrosion resistance of the composite rolled steel plate. In particular, when this rolled composite steel plate is used in high-temperature equipment, even under high-temperature conditions of 300℃, the high-melting-point Ti₂O₃ oxides (melting point of 2130℃) formed due to controlled smelting process can still exist stably in the steel, continuing to function as MC carbide precipitation nuclei. Even free carbon elements present in steel can still react with alloying elements in steel using Ti2O3 oxide as a nucleation core to generate fine MC carbides, thereby further fixing carbon elements, ensuring that carbon elements in carbon steel do not diffuse to the interface, and protecting the corrosion resistance of rolled composite steel plates under long-term high-temperature service conditions.

[0078] The composite steel plate produced by this invention has excellent corrosion resistance and can be effectively used in the energy and chemical industry as a material for manufacturing reaction vessels at room temperature to 300°C. It has great practical significance and a very broad application prospect. Detailed Implementation

[0079] The following will further explain and illustrate the rolled composite steel plate for high-temperature equipment and its manufacturing method according to the present invention with reference to specific embodiments. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0080] The composition of the substrate and cladding of the rolled composite steel plates in the embodiments and comparative examples of this invention is shown in Table 1. The remaining quantities include Fe and other unavoidable impurities. In the embodiments and comparative examples, the cladding material of the rolled composite steel plates is exemplified as austenitic stainless steel. The manufacturing process parameters of the embodiments of this invention are shown in Table 2.

[0081] The manufacturing method of this invention includes the following steps:

[0082] 1) Smelting and casting: Smelting and continuous casting are carried out according to the chemical composition shown in Table 1 to obtain billets. The smelting equipment adopts a 500Kg vacuum induction furnace. First, 410kg of industrial pure iron is added to the vacuum induction furnace. According to the alloy composition ratio of the steel, a certain amount of CaO is added with the furnace (the added CaO is used for slag formation during smelting). Vacuum is drawn, and smelting is carried out under a minimum vacuum degree of about 25Pa. Argon gas is required for atmosphere protection during the smelting process. After the pure iron is melted and cleared, deoxidizers Si+Mn and Al are added in sequence for pre-deoxidation. According to the online monitoring results of the steel composition, the amount of deoxidizer added is finely adjusted and the oxygen level of free oxygen in the steel is controlled at 0.0020~0.0075%. Then, an appropriate amount of Ti is added for final deoxidation. Alloys such as Nb are added for alloying treatment. Finally, B is added, and the billets are cast by top casting method.

[0083] 2) Assembly: The surfaces of the base carbon steel slab and the clad stainless steel slab are processed. The roughness of the mating surface of the two materials is ≤2.0Ra. After surface inspection, it is ensured that there are no surface defects such as oil stains, slag inclusions, and cracks. After welding around the slab, vacuum is drawn with a vacuum degree of 8 to 60 Pa.

[0084] 3) Rolling: The composite slab is heated at 1020-1200℃ and then rolled in two stages. The total cumulative reduction rate of the rolling is not less than 80%, and the final rolling temperature is above 850℃.

[0085] 4) Heat treatment: Quenching and tempering are performed on the rolled composite steel plate. The composite rolled steel plate is quenched at a temperature of 920-955℃ for a holding time of T1 = (1-1.2) H. After holding, it is removed from the furnace and water-cooled to room temperature. Then, it is tempered at a temperature of 550-700℃ for a holding time of T2 = (1-1.5) H. After removing from the furnace, it is air-cooled. T1 and T2 are in minutes, and H is the thickness of the steel plate in mm.

[0086] In this invention, the chemical composition design and related processes of the clad steel plates in Examples 1 to 7 all meet the design specifications of this invention.

[0087] Correspondingly, the composite steel plates of Comparative Examples 1 to 5 were manufactured using the same process steps as those of Examples 1 to 7. The difference was that the alloy element content of the base carbon steel in Comparative Examples 1 to 4 exceeded the design range, while the element content in Comparative Example 5 was within the design range. However, in the smelting and casting operations of step 1) above, the order in which the deoxidizer and alloy B were added was different in Comparative Examples 1 to 5; and the heat treatment tempering process was different.

[0088] Electrolytic samples were taken from the substrate material and the cladding stainless steel side of the bonding interface of the composite steel plates of Examples 1-7 and the control composite steel plates of Comparative Examples 1-5. The MC precipitate phase in the stainless steel was extracted using electrolytic extraction. Precipitates of different sizes were separated by passing them through filter membranes of different particle sizes. The particle size distribution of the precipitates was detected using a laser particle size analyzer, and image analysis software was used to confirm the quantity and size distribution range of the MC precipitate phase (M represents one or more of Nb, Ti, Cr, and Mo) in the steel plates of each example and comparative example. The observed and analyzed data are listed in Table 3 (substrate material) and Table 4 (cladding material at the bonding interface, i.e., the transition layer).

[0089] As shown in Table 3, the total number of precipitates in the composite steel plate substrate materials of Examples 1-7 ranges from 516 to 594, which is significantly higher than the 297 to 319 precipitates in the substrate materials of Comparative Examples 1-5. This indicates that after implementing the technical solution of the present invention, a greater number of MC carbide precipitates can be formed in the substrate material, thereby ensuring the effect of using stable carbides in the substrate to fix free carbon in carbon steel as designed in the technical solution. Moreover, the MC precipitates in the composite steel plate substrate materials of Examples 1-7 are relatively small in size, mainly distributed in the range of 300-600 nm, with an average major axis length of less than 600 nm and a bulk density of greater than 2.0 × 10⁻⁶. 4 pcs / mm 3MC precipitates with a size smaller than 600 nm account for more than 50% of all MC precipitates. When the precipitate size is small, it can, to some extent, pin the growth of austenite grains, thereby refining the grains and further improving the strength and toughness of the material. However, in the carbon steel substrate of the comparative examples 1-5, the MC precipitates are larger, with an average major axis length greater than 800 nm. The main precipitate size distribution ranges above 800 nm, and the proportion of precipitates with a size greater than 1000 nm is relatively high. Their pinning effect on austenite grains is poor, leading to larger grain sizes and affecting the strength and toughness of the steel plate. Because the number of stable precipitates formed in the comparative carbon steel materials is small, the amount of free carbon fixed by the precipitates in the carbon steel is reduced, resulting in a large amount of free carbon segregating towards the bonding interface. This leads to a large number of grain boundary carbides precipitated at the bonding interface cladding material, reducing the corrosion resistance of the cladding material at the bonding interface.

[0090] As shown in Table 4, the number of MC precipitates detected in the composite steel plate cladding materials of Examples 1-7 was 182-244, which is far less than the 424-506 in the comparative examples. Furthermore, the bulk density of the MC precipitates in the transition layer of the cladding materials in the examples was less than 1×10⁻⁶. 4 pcs / mm 3 This indicates that in Examples 1-7, the amount of carbon in the base carbon steel material diffuses into the cladding material through the bonding interface (transition layer) in a smaller quantity, resulting in fewer MCs. In contrast, in Comparative Examples 1-5, a large amount of carbon from the carbon steel material diffuses into the cladding material through the bonding interface, leading to a greater number of carbides in the corresponding cladding materials. Furthermore, Table 4 shows that in Examples 1-7, the average major axis length of the MC precipitates at the bonding interface in the cladding materials is less than 700 nm, and MC precipitates with a size less than 700 nm account for more than 50% of all MC precipitates. Correspondingly, the average size of the MC precipitates obtained in the comparative examples is greater than 850 nm. This further demonstrates that the carbides in the examples have a significantly better effect on fixing free carbon than those in the comparative examples.

[0091] After analyzing the carbide precipitates in the composite steel plates of Examples 1-7 and the comparative steel plates of Comparative Examples 1-5, the mechanical properties and corrosion resistance of the steel plates of Examples 1-7 and Comparative Examples 1-5 were also evaluated. The evaluation results are shown in Table 5. As can be seen from Table 5, the yield strength and tensile strength of the comparative carbon steel substrate are lower than those of the examples. The main reason is that the smelting process, alloy addition sequence, and heat treatment process of the comparative carbon steel substrate are different from those of the examples. As a result, the hardenability of the boron element in the comparative steel cannot be fully utilized. In addition, the different precipitates in the steel have different effects on the microstructure of the steel plate. In the composite steel plate substrate of the present invention, the surface microstructure is 60-80% ferrite (F) and 20-40% pearlite (P), and the core microstructure is 30-40% pearlite and 60-70% ferrite. The smaller precipitates in the examples further refined the austenite grains, which played a certain role in improving the strength and toughness of the steel plate.

[0092] Stainless steel at the interface of the rolled composite steel plates from the examples and comparative examples was subjected to intergranular corrosion testing according to ASTM A262 Practice E. The test results are shown in Table 6. These results indicate that the stainless steel at the interface of the rolled composite steel plates prepared according to the technical requirements of this invention exhibits excellent corrosion resistance. Therefore, among the composite steel plates of Examples 1-7, the corrosion resistance of the clad stainless steel plates in each example is significantly better than that of the comparative example.

[0093] In summary, the composite steel plate of this invention, through optimized design and production process, controls the type, sequence, and amount of deoxidizer added during steel smelting, and performs alloying treatment in a specific order. Combined with a specific production process, this allows for the generation of a large number of dispersed nano-sized MC (M represents one or both of Nb and Ti) precipitates in the steel. These nano-sized MC precipitates can fix the free carbon elements in the base carbon steel, thereby preventing these carbon elements from diffusing excessively to the bonding interface, which would lead to the formation of a large number of carbide precipitates in the stainless steel, resulting in a decrease in the corrosion resistance of the stainless steel. Therefore, using the technical solution of this invention can ensure the strength and toughness of the carbon steel base material, while also significantly improving the corrosion resistance of the rolled composite steel plate, ensuring the safety performance of the rolled composite steel plate during long-term high-temperature service.

[0094] Furthermore, it should be noted that the combination of the various technical features in this invention is not limited to the combination methods described in the claims of this invention or the combination methods described in the specific embodiments. All technical features described in this invention can be freely combined or combined in any way, unless they contradict each other.

[0095] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

[0096]

[0097]

[0098]

[0099]

[0100]

[0101]

[0102]

Claims

1. A corrosion-resistant rolled composite steel plate, comprising a substrate, a cladding layer, and a transition layer between the substrate and the cladding layer, wherein, The substrate composition by weight percentage is as follows: C: 0.01%–0.10%, Si: 0.2%–0.7%, Mn: 0.30%–1.70%, Ti: 0.006%–0.012%, Als: 0.008%–0.018%, Nb: 0.0090%–0.050%, B: 0.0010%–0.0050%, N: 0.0015%–0.0050%, P≤0.017%, S≤0.020%, O≤0.0050%, with the balance including Fe and other unavoidable impurities; The surface microstructure of the composite steel plate substrate consists of 60–80% ferrite + 20–40% pearlite + MC precipitates, while the central microstructure consists of 30–40% pearlite + 60–70% ferrite + MC precipitates. Here, M represents one or both of Nb and Ti, the average major axis length of the MC precipitates is less than 600 nm, and the bulk density of MC precipitates with a major axis length less than 600 nm is greater than 2.0 × 10⁻⁶. 4 pcs / mm 3 ; The composite steel plate cladding is made of stainless steel, and its microstructure contains MC precipitates, where M represents one or more of Cr, Mo, Nb, and Ti. The average major axis length of the MC precipitates is less than 700 nm, and the bulk density of the MC precipitates is less than 1.0 × 10⁻⁶. 4 pcs / mm 3 .

2. The corrosion-resistant rolled composite steel plate as described in claim 1, characterized in that, The composite steel plate substrate composition contains Fe and other unavoidable impurities in the remainder.

3. The corrosion-resistant rolled composite steel plate as described in claim 1 or 2, characterized in that, The composite steel plate substrate also contains at least one of the following chemical elements: 0 < Ca ≤ 0.0055%, 0 < Ni ≤ 0.65%, and 0 < Cu ≤ 0.55%.

4. The corrosion-resistant rolled composite steel plate as described in claim 1 or 2, characterized in that, In the composite steel plate substrate, the proportion of MC precipitates with a long axis length of less than 600 nm to the total number of MC precipitates is greater than 50%.

5. The corrosion-resistant rolled composite steel plate as described in claim 3, characterized in that, In the composite steel plate substrate, the proportion of MC precipitates with a long axis length of less than 600 nm to the total number of MC precipitates is greater than 50%.

6. The corrosion-resistant rolled composite steel plate as described in claim 1 or 2, characterized in that, In the composite steel plate cladding, the proportion of MC precipitates with a long axis length of less than 700 nm to the total number of MC precipitates is greater than 50%.

7. The corrosion-resistant rolled composite steel plate as described in claim 3, characterized in that, In the composite steel plate cladding, the proportion of MC precipitates with a long axis length of less than 700 nm to the total number of MC precipitates is greater than 50%.

8. The corrosion-resistant rolled composite steel plate as described in claim 4, characterized in that, In the composite steel plate cladding, the proportion of MC precipitates with a long axis length of less than 700 nm to the total number of MC precipitates is greater than 50%.

9. The corrosion-resistant rolled composite steel plate as described in claim 5, characterized in that, In the composite steel plate cladding, the proportion of MC precipitates with a long axis length of less than 700 nm to the total number of MC precipitates is greater than 50%.

10. The corrosion-resistant rolled composite steel plate as described in claim 1 or 2, characterized in that, The microstructure of the composite steel plate cladding also contains a very small amount of σ phase, with the proportion of σ phase ≤ 1.5%.

11. The corrosion-resistant rolled composite steel plate as described in claim 3, characterized in that, The microstructure of the composite steel plate cladding also contains a very small amount of σ phase, with the proportion of σ phase ≤ 1.5%.

12. The corrosion-resistant rolled composite steel plate as described in claim 4, characterized in that, The microstructure of the composite steel plate cladding also contains a very small amount of σ phase, with the proportion of σ phase ≤ 1.5%.

13. The corrosion-resistant rolled composite steel plate as described in claim 6, characterized in that, The microstructure of the composite steel plate cladding also contains a very small amount of σ phase, with the proportion of σ phase ≤ 1.5%.

14. The corrosion-resistant rolled composite steel plate as described in claim 7, characterized in that, The microstructure of the composite steel plate cladding also contains a very small amount of σ phase, with the proportion of σ phase ≤ 1.5%.

15. The corrosion-resistant rolled composite steel plate as described in claim 8, characterized in that, The microstructure of the composite steel plate cladding also contains a very small amount of σ phase, with the proportion of σ phase ≤ 1.5%.

16. The corrosion-resistant rolled composite steel plate as described in claim 9, characterized in that, The microstructure of the composite steel plate cladding also contains a very small amount of σ phase, with the proportion of σ phase ≤ 1.5%.

17. The corrosion-resistant rolled composite steel plate as described in claim 10, characterized in that, The proportion of σ phase near the transition layer is ≤0.5%.

18. The corrosion-resistant rolled composite steel plate as described in claim 11, characterized in that, The proportion of σ phase near the transition layer is ≤0.5%.

19. The corrosion-resistant rolled composite steel plate as described in claim 12, characterized in that, The proportion of σ phase near the transition layer is ≤0.5%.

20. The corrosion-resistant rolled composite steel plate as described in claim 13, characterized in that, The proportion of σ phase near the transition layer is ≤0.5%.

21. The corrosion-resistant rolled composite steel plate as described in claim 14, characterized in that, The proportion of σ phase near the transition layer is ≤0.5%.

22. The corrosion-resistant rolled composite steel plate as described in claim 15, characterized in that, The proportion of σ phase near the transition layer is ≤0.5%.

23. The corrosion-resistant rolled composite steel plate as described in claim 16, characterized in that, The proportion of σ phase near the transition layer is ≤0.5%.

24. The corrosion-resistant rolled composite steel plate as described in claim 1 or 2, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

25. The corrosion-resistant rolled composite steel plate as described in claim 3, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

26. The corrosion-resistant rolled composite steel plate as described in claim 4, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

27. The corrosion-resistant rolled composite steel plate as described in claim 5, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

28. The corrosion-resistant rolled composite steel plate as described in claim 6, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

29. The corrosion-resistant rolled composite steel plate as described in claim 7, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

30. The corrosion-resistant rolled composite steel plate as described in claim 8, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

31. The corrosion-resistant rolled composite steel plate as described in claim 9, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

32. The corrosion-resistant rolled composite steel plate as described in claim 10, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

33. The corrosion-resistant rolled composite steel plate as described in claim 11, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

34. The corrosion-resistant rolled composite steel plate as described in claim 12, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

35. The corrosion-resistant rolled composite steel plate as described in claim 13, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

36. The corrosion-resistant rolled composite steel plate as described in claim 14, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

37. The corrosion-resistant rolled composite steel plate as described in claim 15, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

38. The corrosion-resistant rolled composite steel plate as described in claim 16, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

39. The corrosion-resistant rolled composite steel plate as described in claim 17, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

40. The corrosion-resistant rolled composite steel plate as described in claim 18, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

41. The corrosion-resistant rolled composite steel plate as described in claim 19, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

42. The corrosion-resistant rolled composite steel plate as described in claim 20, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

43. The corrosion-resistant rolled composite steel plate as described in claim 21, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

44. The corrosion-resistant rolled composite steel plate as described in claim 22, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

45. The corrosion-resistant rolled composite steel plate as described in claim 23, characterized in that, The thickness of the composite steel plate substrate is ≥6mm, and the thickness of the cladding layer is ≥2mm.

46. ​​The corrosion-resistant rolled composite steel plate as described in claim 24, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

47. The corrosion-resistant rolled composite steel plate as described in claim 25, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

48. The corrosion-resistant rolled composite steel plate as described in claim 26, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

49. The corrosion-resistant rolled composite steel plate as described in claim 27, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

50. The corrosion-resistant rolled composite steel plate as described in claim 28, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

51. The corrosion-resistant rolled composite steel plate as described in claim 29, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

52. The corrosion-resistant rolled composite steel plate as described in claim 30, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

53. The corrosion-resistant rolled composite steel plate as described in claim 31, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

54. The corrosion-resistant rolled composite steel plate as described in claim 32, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

55. The corrosion-resistant rolled composite steel plate as described in claim 33, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

56. The corrosion-resistant rolled composite steel plate as described in claim 34, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

57. The corrosion-resistant rolled composite steel plate as described in claim 35, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

58. The corrosion-resistant rolled composite steel plate as described in claim 36, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

59. The corrosion-resistant rolled composite steel plate as described in claim 37, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

60. The corrosion-resistant rolled composite steel plate as described in claim 38, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

61. The corrosion-resistant rolled composite steel plate as described in claim 39, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

62. The corrosion-resistant rolled composite steel plate as described in claim 40, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

63. The corrosion-resistant rolled composite steel plate as described in claim 41, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

64. The corrosion-resistant rolled composite steel plate as described in claim 42, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

65. The corrosion-resistant rolled composite steel plate as described in claim 43, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

66. The corrosion-resistant rolled composite steel plate as described in claim 44, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

67. The corrosion-resistant rolled composite steel plate as described in claim 45, characterized in that, The thickness of the transition layer of the composite steel plate substrate is ≤230μm.

68. The corrosion-resistant rolled composite steel plate as described in claim 1 or 2, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

69. The corrosion-resistant rolled composite steel plate as described in claim 3, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

70. The corrosion-resistant rolled composite steel plate as described in claim 4, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

71. The corrosion-resistant rolled composite steel plate as described in claim 5, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

72. The corrosion-resistant rolled composite steel plate as described in claim 6, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

73. The corrosion-resistant rolled composite steel plate as described in claim 7, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

74. The corrosion-resistant rolled composite steel plate as described in claim 8, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

75. The corrosion-resistant rolled composite steel plate as described in claim 9, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

76. The corrosion-resistant rolled composite steel plate as described in claim 10, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

77. The corrosion-resistant rolled composite steel plate as described in claim 11, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

78. The corrosion-resistant rolled composite steel plate as described in claim 12, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

79. The corrosion-resistant rolled composite steel plate as described in claim 13, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

80. The corrosion-resistant rolled composite steel plate as described in claim 14, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

81. The corrosion-resistant rolled composite steel plate as described in claim 15, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

82. The corrosion-resistant rolled composite steel plate as described in claim 16, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

83. The corrosion-resistant rolled composite steel plate as described in claim 17, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

84. The corrosion-resistant rolled composite steel plate as described in claim 18, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

85. The corrosion-resistant rolled composite steel plate as described in claim 19, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

86. The corrosion-resistant rolled composite steel plate as described in claim 20, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

87. The corrosion-resistant rolled composite steel plate as described in claim 21, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

88. The corrosion-resistant rolled composite steel plate as described in claim 22, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

89. The corrosion-resistant rolled composite steel plate as described in claim 23, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

90. The corrosion-resistant rolled composite steel plate as described in claim 24, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

91. The corrosion-resistant rolled composite steel plate as described in claim 25, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

92. The corrosion-resistant rolled composite steel plate as described in claim 26, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

93. The corrosion-resistant rolled composite steel plate as described in claim 27, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

94. The corrosion-resistant rolled composite steel plate as described in claim 28, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

95. The corrosion-resistant rolled composite steel plate as described in claim 29, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

96. The corrosion-resistant rolled composite steel plate as described in claim 30, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

97. The corrosion-resistant rolled composite steel plate as described in claim 31, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

98. The corrosion-resistant rolled composite steel plate as described in claim 32, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

99. The corrosion-resistant rolled composite steel plate as described in claim 33, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

100. The corrosion-resistant rolled composite steel plate as described in claim 34, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

101. The corrosion-resistant rolled composite steel plate as described in claim 35, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

102. The corrosion-resistant rolled composite steel plate as described in claim 36, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

103. The corrosion-resistant rolled composite steel plate as described in claim 37, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

104. The corrosion-resistant rolled composite steel plate as described in claim 38, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

105. The corrosion-resistant rolled composite steel plate as described in claim 39, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

106. The corrosion-resistant rolled composite steel plate as described in claim 40, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

107. The corrosion-resistant rolled composite steel plate as described in claim 41, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

108. The corrosion-resistant rolled composite steel plate as described in claim 42, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

109. The corrosion-resistant rolled composite steel plate as described in claim 43, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

110. The corrosion-resistant rolled composite steel plate as described in claim 44, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

111. The corrosion-resistant rolled composite steel plate as described in claim 45, characterized in that, The composite steel plate substrate has a yield strength ≥255MPa, tensile strength ≥390MPa, reduction of area ≥60%, elongation ≥20%, impact absorption energy at -20℃ ≥200J, and impact absorption capacity at -40℃ ≥120J; the substrate grain size grade is not less than 6.0; and the shear strength of the composite steel plate is ≥280MPa.

112. The corrosion-resistant rolled composite steel plate as described in claim 1, characterized in that, The stainless steel cladding of the composite steel plate is austenitic stainless steel, ferritic stainless steel, or duplex stainless steel.

113. The method for manufacturing the corrosion-resistant rolled composite steel plate according to any one of claims 1 to 112, characterized in that, Includes the following steps: 1) Smelting and casting to obtain base material and multilayered billet. The composite steel plate is smelted and cast to obtain a base material billet; during the smelting process, Mn+Si and Al are added sequentially for pre-deoxidation. After pre-deoxidation, the oxygen content of the molten steel is 0.0020% to 0.0075%. Then Ti is added for final deoxidation. After deoxidation, element B is added. The base material billet is obtained after casting. At the same time, a stainless steel clad billet is also obtained. 2) Billet assembly After surface treatment of the base casting billet and the cladding billet, they are stacked together. The perimeter of the stacked casting billet is welded and sealed, vacuumed, and sealed again to form a composite slab. Composite slab rolling The composite slab is heated to 1020-1200℃ and then rolled in two stages. The total reduction rate of the composite slab in the first stage rolling is not less than 60%, the total reduction rate in the second stage rolling is not less than 20%, and the reduction rate in the last pass is 8-18%. The total reduction rate of the two stages rolling is not less than 80%, and the final rolling temperature is above 850℃. 3) Heat treatment: Quenching and tempering are performed on the composite steel plate.

114. The method for manufacturing the corrosion-resistant rolled composite steel plate as described in claim 113, characterized in that, In step 2), the surfaces of the substrate and the clad casting are surface treated to ensure that there are no obvious oil stains, slag inclusions, cracks or other surface defects on the casting surface, and at the same time, the roughness of the machined surface of the casting must not exceed 2.0Ra.

115. The method for manufacturing the corrosion-resistant rolled composite steel plate as described in claim 113, characterized in that, In step 4), the quenching temperature is 920~955℃, the quenching holding time is T1=(1~1.2)H, and after the holding time is completed, the plate is taken out of the furnace and water-cooled to room temperature. Here, T1 is in min and H is the thickness of the steel plate in mm.

116. The method for manufacturing corrosion-resistant rolled composite steel plate as described in claim 113 or 115, characterized in that, In step 4), the tempering temperature is 550-700℃, and the tempering holding time is T2 = (1-1.5)H, where T2 is in min and H is the thickness of the steel plate in mm.

117. The method for manufacturing the corrosion-resistant rolled composite steel plate as described in claim 113, characterized in that, In step 2), the vacuum level is 8-60 Pa after the vacuum is drawn.

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