Corrosion-resistant rolled clad steel plate and manufacturing method therefor

Abstract

A corrosion-resistant rolled composite steel plate and a manufacturing method therefor. The corrosion-resistant rolled composite steel plate comprises a base material, a cladding layer, and a transition layer between the base material and the cladding layer; in percentage by weight, the base material is prepared from the following components: 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%, and the balance being Fe and other unavoidable impurities; and the cladding layer is stainless steel. By preventing or reducing the diffusion of carbon on a carbon steel side of the base material at an interface of the clad steel plate, the possibility of failure caused by intergranular corrosion of the stainless steel at the cladding layer side is reduced, the corrosion resistance and the safety of the rolled clad steel plate in high temperature operating environments are comprehensively improved, and the present invention is suitable for equipment at operating temperatures of approx. 300°C in energy fields such as electrical power and the chemical industry.

Description

Corrosion-resistant rolled composite steel plate and manufacturing method thereof Technical Field

[0001] The present invention relates to corrosion-resistant steel and a manufacturing method thereof, in particular to a corrosion-resistant rolled composite steel plate and a manufacturing method thereof, which is suitable for equipment in the working temperature range of room temperature to 300°C in energy industries such as electric power and chemical industry. Background Art

[0002] Composite steel plates composed of low-alloy steel and various corrosion-resistant materials are frequently used in industries such as crude oil processing and the energy and chemical industry due to their high mechanical strength and strong corrosion resistance. With the rapid development of the national economy, the demand for various energy-related raw materials, such as petroleum and fertilizers, is increasing. To improve energy production efficiency, energy production and processing equipment must be larger, more highly parameterized (higher temperatures and pressures), and lighter. This demand for equipment upgrades places higher demands on the performance of the steel plates used in manufacturing equipment, requiring not only higher strength and hardness, but also excellent toughness, formability, and corrosion resistance.

[0003] The traditional production process of composite steel plates is the explosive composite process. The main problem of this production process is that when using explosives for explosive composite, a large amount of harmful gases will be generated, which will have an adverse impact on the environment. That is, this type of production process does not meet environmental protection requirements; at the same time, the bonding rate at the interface of the explosive composite steel plate is low, sometimes failing to meet the bonding rate requirement of more than 97%. When this type of steel plate is used to manufacture various high-temperature, high-pressure, and large-scale container equipment, there will be a major safety hazard. Once the composite steel plate joints are separated and the equipment fails, it will have a huge impact on the safety of personnel and property.

[0004] Compared with explosive clad steel plates, the bonding rate of rolled clad steel plates is greatly improved to over 99%, and the production process is more environmentally friendly than explosive cladding. Therefore, in recent years, the production scale and engineering application of rolled clad steel plates have been expanding year by year.

[0005] However, whether it is explosive composite steel or rolled composite steel, a transition layer forms at the interface between the carbon steel and other corrosion-resistant materials. Especially when the steel plate is subjected to long-term service at high temperatures, the carbon in the carbon steel substrate diffuses through the transition layer into the composite stainless steel. Once a large amount of carbides forms in the composite stainless steel, intergranular corrosion occurs, which adversely affects the corrosion resistance of the composite corrosion-resistant material, ultimately causing the composite material to fail and posing a safety hazard.

[0006] Therefore, how to reasonably design the alloy composition and production process of the carbon steel base layer to minimize the negative impact on the corrosion resistance of the corrosion-resistant material caused by the diffusion of carbon elements in the carbon steel material through the transition layer to the composite 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] Prior art, such as Chinese patent application publication number CN107310218A, discloses a composite bulletproof steel plate and its manufacturing method. The composite bulletproof steel plate comprises hard and soft steel layers spaced apart from each other. The surface layer of the composite bulletproof steel plate is the hard steel layer, and the hard and soft steel layers are atomically bonded by rolling. The chemical element weight percentages of the soft steel layer are as follows: 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 remainder being Fe and other unavoidable impurities. The composite bulletproof steel plate comprises multiple layers of soft and hard steel layers. When impacted by a projectile, the hard steel layer breaks into small fragments, dissipating the impact energy. Simultaneously, the soft steel layer redirects the bullet's travel direction, increasing its forward resistance, thereby providing enhanced bulletproofing. The core technical solution of this invention is to effectively dissipate the kinetic energy of a bullet by arranging layers of high-strength hard steel and high-toughness soft steel alternately. However, the invention's technical solution does not address the transition interface between the hard and soft steel layers, nor does it address the diffusion of carbon from the carbon steel into the composite material.

[0008] Chinese patent application publication number CN107310219A discloses a "bullet-proof steel plate with excellent cold-bending performance and its manufacturing method." The plate comprises three soft steel layers and two hard steel layers, spaced apart from each other. The soft steel layer forms the surface layer of the plate, and the hard and soft steel layers are atomically bonded by rolling. The chemical elements in the soft steel layer are as follows: 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 remainder being Fe and other unavoidable impurities. The hard steel layer deflects the projectile's trajectory, while the soft steel layer on the surface exhibits excellent plasticity, ensuring it resists cracking during deformation. Upon impact, it breaks into small fragments, dissipating the impact energy. Simultaneously, the soft steel layer in the core deflects the bullet's trajectory, increasing its resistance and providing enhanced ballistic protection. This patent application also utilizes a staggered arrangement of hard and soft steel to reduce the projectile's kinetic energy. The technical solution does not address the bonding interface of the rolled composite steel plates or element diffusion.

[0009] Chinese patent application publication number CN108231273A discloses a method for improving the interface of a copper-aluminum composite material, comprising the following steps: pre-coating or depositing graphene at the copper-aluminum interface, and then processing and compounding the copper, aluminum, and graphene; the coating or deposition method is one of painting, electroplating, and chemical vapor deposition; the processing and compounding method is one of rolling compounding, extrusion compounding, and drawing compounding; and the graphene is a powder or film. Using the method of the present invention, graphene is added to the copper-aluminum interface, which can ensure interfacial bonding and improve the interface bonding and conductivity while preventing the formation of brittle and poorly conductive intermetallic compounds at the interface. This patent application involves a method for improving the interface position of a composite material, but because the substrate and composite material of the composite material are copper and aluminum, respectively, it has little reference value for carbon steel and stainless steel composite rolling technology. The patent application also does not mention the impact of element diffusion at the interface on material properties.

[0010] Based on the above patent applications, in the existing rolled composite steel plate technology, there is little consideration for the transition layer at the interface between the base and the composite material, especially the influence of the elements in the base material through the transition layer on the performance of the composite stainless steel. Basically, no targeted measures have been taken to reduce the possibility of weakening the corrosion resistance of stainless steel due to the precipitation of carbides at the interface of the composite material. Especially in the chemical and energy industries, many times, the operating temperature of composite steel plate manufacturing equipment is at high temperature (within 300°C). If the equipment is operated at high temperature for decades, the elements at the material interface may diffuse again, especially the carbon elements on the carbon steel side will diffuse into the stainless steel composite layer, which will form more carbides, further reducing the corrosion resistance of stainless steel and posing a potential accident hazard.

[0011] Summary of the Invention

[0012] The purpose of the present invention is to provide a corrosion-resistant rolled composite steel plate and a manufacturing method thereof. 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 intergranular corrosion and failure of the stainless steel on the composite side is reduced, and the corrosion resistance and safety performance of the rolled composite steel plate under high-temperature working conditions are comprehensively improved. The rolled composite steel plate is suitable for use in equipment with an operating temperature of room temperature to 300°C in energy industries such as electricity and chemical industry.

[0013] To achieve the above object, the technical solution of the present invention is:

[0014] A large number of finely dispersed MC (M represents one or more of Nb and Ti) precipitation phases with stable high-temperature performance are formed in the composite steel plate substrate of the present invention. These stable carbide precipitation phases can fix the free carbon element in the steel in the substrate carbon steel, thereby preventing the carbon element in the carbon steel from diffusing and migrating to the interface of the rolled composite steel plate under high-temperature working conditions, resulting in an increase in the carbon element concentration in the stainless steel near the interface, and the generation of a large number of carbide precipitation phases at the stainless steel grain boundaries, which induces intergranular corrosion and ultimately weakens or even loses the corrosion protection function of the composite material.

[0015] Specifically, the corrosion-resistant rolled composite steel plate of the present invention is formed by composite rolling of carbon steel as a base material and stainless steel as a clad layer. Therefore, the corrosion-resistant rolled composite steel plate of the present invention comprises a base material layer, a clad layer, and a transition layer between the base material layer and the clad layer; wherein the base material layer comprises the following components by weight: C: 0.01% to 0.10%, Si: 0.20% to 0.70%, Mn: 0.30% to 1.70%, Ti: 0.006% to 0.012%, Als: 0.008% to 0.018%, Nb: 0.0090% to 0.050%, B: 0.0010% to 0.0050%, N: 0.0015% to 0.0050%, P ≤ 0.017%, S ≤ 0.020%, O ≤ 0.0050%, and the balance comprises Fe and other unavoidable impurities;

[0016] The surface microstructure of the substrate layer is ferrite with an area percentage of 60-80% + pearlite with an area percentage of 20-40% + MC precipitation phase, and the central microstructure of the substrate layer is pearlite with an area percentage of 30-40% + ferrite with an area percentage of 60-70% + MC precipitation phase; wherein M represents one or both of Nb and Ti, the average major axis length of the MC precipitation phase is less than 600 nm, and the volume density of the MC precipitation phase with a major axis length less than 600 nm is greater than or equal to 2.0×10 4 Pieces / mm 3 ;

[0017] The microstructure of the composite layer contains MC precipitates, wherein 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 volume density of the MC precipitates is less than 1.0×10 4 Pieces / mm 3 .

[0018] Furthermore, the balance of the composite steel plate base material components is Fe and other inevitable impurities.

[0019] Furthermore, the composite steel plate base material also contains at least one of the following chemical elements: 0<Ca≤0.0055%, 0<Ni≤0.65%, 0<Cu≤0.55%.

[0020] Preferably, in the composite steel plate substrate layer, the MC precipitates with a major axis length of less than 600 nm account for more than 50% of the total MC precipitates. Preferably, in the composite steel plate substrate layer, the MC precipitates with a major axis length of less than 600 nm account for ≥ 60% of the total MC precipitates.

[0021] Preferably, the stainless steel described herein can be any of various stainless steels well known in the art, including but not limited to austenitic stainless steel, ferritic stainless steel, duplex stainless steel, or super stainless steel. The present invention can be implemented using readily available stainless steel products, or stainless steel can be prepared independently for use as the composite casting slab of the present invention.

[0022] In some embodiments, the weight percentages of the components of the stainless steel are: C: 0.01-0.05%; Si: 0.50-0.80%; Mn: 1.10-1.50%; Ni: 6.5-9.5%; Cr: 15.0-22.0%; N: 0.060-0.120%; P: ≤0.015%; S: ≤0.005%; O: ≤0.005%; the balance is Fe and other unavoidable impurities.

[0023] Preferably, in the composite steel plate cladding, the MC precipitates with a major axis length of less than 700 nm account for more than 50% of the total MC precipitates. Preferably, in the composite steel plate cladding, the MC precipitates with a major axis length of less than 700 nm account for ≥55% of the total MC precipitates.

[0024] Furthermore, a very small amount of σ phase exists in the microstructure of the composite steel plate cladding layer, and the area ratio of the σ phase is ≤1.5%. Preferably, the area ratio of the σ phase near the transition layer is ≤0.5%.

[0025] Preferably, the thickness of the substrate layer of the composite steel plate is ≥6 mm, the thickness of the cladding layer is 2 mm, and preferably, the thickness of the transition layer is ≤230 μm. In some embodiments, the thickness of the substrate layer is 6 to 200 mm. In some embodiments, the thickness of the substrate layer is 10 to 200 mm or 10 to 100 mm. In some embodiments, the thickness of the cladding layer is 2 to 20 mm. In some embodiments, the thickness of the transition layer is 1 to 230 μm. In some embodiments, the thickness of the transition layer is 1 to 150 μm. In some embodiments, the thickness of the transition layer is 1 to 50 μm. Herein, the thickness of the base layer and the cladding layer is measured in accordance with GB / T 6396-2008, and the thickness of the transition layer is measured in accordance with GB / T 6462-2005.

[0026] The composite steel plate substrate of the present invention has a yield strength of ≥255MPa, a tensile strength of ≥390MPa, a cross-sectional shrinkage of ≥60%, an elongation of ≥20%, an impact absorption energy of ≥200J at -20°C, and an impact absorption capacity of ≥120J at -40°C; and the shear strength of the composite steel plate is ≥280MPa.

[0027] In some embodiments, the substrate layer of the composite steel plate of the present invention has a yield strength of ≥280 MPa. In some embodiments, the substrate layer of the composite steel plate of the present invention has a yield strength of ≥300 MPa. In some embodiments, the substrate layer of the composite steel plate of the present invention has a yield strength between 255 and 400 MPa, such as between 280 and 400 MPa.

[0028] In some embodiments, the tensile strength of the substrate layer of the composite steel plate of the present invention is ≥ 410 MPa. In some embodiments, the tensile strength of the substrate layer of the composite steel plate of the present invention is ≥ 430 MPa. In some embodiments, the tensile strength of the substrate layer of the composite steel plate of the present invention is between 390 and 500 MPa, or between 410 and 500 MPa.

[0029] In some embodiments, the cross-sectional shrinkage of the substrate layer of the composite steel plate of the present invention is ≥70%. In some embodiments, the cross-sectional shrinkage of the substrate layer of the composite steel plate of the present invention is between 60% and 80% or between 70% and 80%.

[0030] In some embodiments, the elongation of the substrate layer of the composite steel plate of the present invention is ≥ 23%. In some embodiments, the elongation of the substrate layer of the composite steel plate of the present invention is between 20% and 27%, such as between 23% and 27%.

[0031] In some embodiments, the -20°C impact absorbed energy of the substrate layer of the composite steel plate of the present invention is greater than 230 J. In some embodiments, the -20°C impact absorbed energy of the substrate layer of the composite steel plate of the present invention is between 200 and 260 J, such as between 230 and 260 J.

[0032] In some embodiments, the -40°C impact absorption energy of the substrate layer of the composite steel plate of the present invention is between 120 and 150 J.

[0033] In some embodiments, the shear strength at the composite interface of the substrate layer of the composite steel plate of the present invention is ≥300 MPa. In some embodiments, the shear strength at the composite interface of the substrate layer of the composite steel plate of the present invention is between 280 and 360 MPa.

[0034] In the composition design of the composite steel plate substrate layer of the present invention:

[0035] C: C is an important strengthening element. To ensure that the carbon steel plate has appropriate strength, the mass percentage of C in the steel needs to be controlled to be greater than or equal to 0.01%. At the same time, in order to improve the welding performance of the carbon steel material in the base layer, it is necessary to control the upper limit of the C content in the carbon steel. In addition, if the carbon content in the carbon steel base layer is high, the difference in carbon concentration gradients between the two materials will cause large-scale carbon migration at the interface between the base layer and the stainless steel cladding material, causing intergranular corrosion of the stainless steel. Therefore, the upper limit is controlled to 0.10%. Accordingly, based on this, the present invention controls the C content to 0.01% to 0.10%.

[0036] Si: Similar to carbon, Si is a commonly used strengthening element in low-alloy steels. Adding a certain amount of Si to steel can improve its strength. Si is also a weak deoxidizer, assisting in deoxidation during the smelting process. Most of the SiO2 formed after deoxidation is removed from the slag and does 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 and the formation of MC precipitation phases. It also immobilizes carbon in the steel and prevents large-scale carbon diffusion. Therefore, a certain amount of Si is necessary for steel. However, excessive Si can reduce the steel's weldability. Because Si binds more strongly with oxygen than iron does, it easily forms low-melting-point silicates during welding. These increase the fluidity of the slag and molten metal, causing spattering and affecting the quality of the welded joint. Therefore, controlling the Si content within a certain range can help improve the weldability of steel. Therefore, the present invention controls the Si content to 0.20% to 0.70%.

[0037] Mn: Mn is also an important strengthening element that 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 steel, the lower limit of Mn is 0.30%. However, Mn is very likely to cause central segregation in steel. Excessive addition of Mn will cause serious segregation at the center of the thickness of the steel plate, reducing the low-temperature toughness of the core of the steel plate. Therefore, the upper limit of the Mn content is limited to 1.70%. Based on this, the present invention controls the Mn content to 0.30% to 1.70%.

[0038] Ti: Ti is both a deoxidizing element and a strong carbide- and nitride-forming element. In the present invention, adding an appropriate amount of Ti can, on the one hand, form a stable MC precipitate phase in the steel, fixing the carbon in the substrate layer and preventing it from diffusing to the composite material interface. Simultaneously, some of the Ti helps fix the free nitrogen in the steel, forming a TiN precipitate phase. This TiN precipitate can inhibit the growth of austenite grains, refine the grains, and thus simultaneously improve the strength and toughness of the steel plate. Ti fixes some of the free nitrogen, helping to ensure that the boron in the steel remains free, improving the hardenability of the steel. Furthermore, Ti deoxidizes the steel to form Ti2O3 particles, which promote the formation of intragranular ferrite and enhance the steel's low-temperature impact toughness. However, when the Ti content in the steel is too high, the resulting TiN and Ti2O3 particles become larger, no longer hindering austenite growth and the formation of intragranular ferrite. Instead, they become a source of crack initiation, reducing the steel's low-temperature impact toughness. Therefore, the upper limit of Ti is 0.012%. Based on this, the present invention controls the Ti content to 0.006% to 0.012%.

[0039] Als: Al is first and foremost an important deoxidizing element, forming aluminum oxide inclusions. Furthermore, Al can combine with nitrogen in steel to form AlN precipitates, reducing the free nitrogen content in the steel. This prevents the combination of boron and nitrogen in the steel, promotes an increase in the free boron content in the steel, improves the hardenability of the steel, and contributes to improving the strength of the steel plate. However, when the acid-soluble aluminum content in the steel is too high, the size of its deoxidation product, aluminum oxide, will increase. Furthermore, since aluminum oxide inclusions have strong adsorption capacity, large-sized aluminum oxide clusters will form. These can clog the water inlet during steelmaking, affecting the casting process of the molten steel. If these large-sized clustered inclusions enter the steel plate, they will cause the steel plate to fail inclusion ratings and flaw detection. Therefore, the present invention controls the acid-soluble Als content to 0.008% to 0.018%.

[0040] Nb: Nb is a strong carbide-forming element. It combines with carbon in steel to form MC precipitates, stabilizing the carbon in the steel and preventing it from diffusing to the interface. Adding an appropriate amount of Nb can also increase the recrystallization temperature of the steel. After recrystallization rolling in the austenite region, the austenite grains will not grow rapidly, resulting in fine-grained steel with higher strength and toughness. However, excessive Nb content in the steel can lead to larger MC precipitates, which in turn reduces the toughness of the steel plate and worsens the toughness of the weld heat-affected zone. Therefore, the present invention controls the Nb content to between 0.0090% and 0.050%.

[0041] B: The addition of an appropriate amount of B element is to compensate for the decrease in the strength performance of the steel plate due to the reduction in the content of solid-solution carbon in the steel after the carbon element in the steel is fixed by stable carbides. If the B element in the steel exists in a free state, some of the B will preferentially occupy the grain boundary position, thereby improving the hardenability of the steel plate. Therefore, the premise for the B element to play its role is that B must exist in the steel in a free state. Therefore, in order to prevent the B in the steel from combining with oxygen and nitrogen to form boron oxide and boron nitride, the oxygen content and nitrogen content in the steel must be well controlled, which is also a key point in the design of the alloy composition. However, it should be noted that if excessive B is added to the steel, the excessive B will easily form a large amount of segregation at the grain boundaries, which will be detrimental to the toughness of the steel. Therefore, the present invention controls the B content to 0.0010%≤B≤0.0050%.

[0042] N: A proper amount of Ti and Al elements are added. These two elements can form TiN and AlN precipitation phases with the N element in the steel. When these precipitation phases are small and dispersed, they can refine the austenite grains, thereby improving the strength and toughness of the steel plate. However, when the N content in the steel is too high, the excess N element will combine with the B element in the steel to form BN, consuming the free B element in the steel and reducing the effect of the B element on improving the strength of the steel plate. At the same time, too much N element will have an adverse effect on the toughness of the steel, especially when the solid solution N content exceeds 0.005%, the low-temperature toughness of the steel plate will be significantly reduced. Therefore, the present invention controls the N content to 0.0015 <N<0.0050%。

[0043] Preferably, the composite steel plate substrate layer of the present invention further contains at least one of the following chemical elements: 0<Ca≤0.0055%, 0<Ni<0.65%, 0<Cu≤0.55%.

[0044] 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 element B. However, when the Ca content in steel exceeds 0.0055%, it is easy to form large inclusions of calcium oxide and calcium sulfide in the steel, which is detrimental to the toughness of the steel. Therefore, the present invention controls the Ca content to 0 <Ca≤0.0055%。

[0045] Ni: Ni is a typical austenite stabilizing element that can significantly improve the hardenability of steel plates and also improve the low-temperature toughness of steel plates. However, the price of Ni is relatively high. Considering the production cost of steel, it is not advisable to add excessive Ni to steel. Therefore, the present invention controls the Ni content to 0 <Ni<0.65%。

[0046] Cu: Adding an appropriate amount of Cu element helps to improve the strength of steel and improve the corrosion resistance of steel. However, when the Cu content in steel is too high, the steel plate is prone to high temperature brittleness at high temperatures. Therefore, the present invention controls the Cu content to 0 <Cu≤0.55%。

[0047] 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 the performance and cost control, in the technical solution of the present invention, at least one of the above-mentioned elements can be preferably added.

[0048] Inevitable impurities exist in the base material layer of the composite steel plate of the present invention, with P≤0.017%, S≤0.020%, and O≤0.0050%.

[0049] P, S and O are all impurity elements in steel. When technical conditions permit, in order to obtain steel with better performance and higher quality, the content of impurity elements in steel should be reduced as much as possible.

[0050] P: P is a harmful element for most steel plates. This is primarily because it easily segregates toward grain boundaries, reducing the bonding strength between atoms there and causing temper brittleness in the steel. This temper brittleness is particularly exacerbated when the steel is operated at high temperatures. Therefore, the present invention limits the P content to ≤ 0.017%.

[0051] S: The S element in steel easily combines with the Mn element in the steel, forming MnS inclusions. The higher the S content, the larger the MnS inclusions, which negatively impacts the strength and toughness of the steel plate. Excessive S content also leads to central segregation in the slab and can easily cause hot cracking. Therefore, the present invention controls the S content to ≤ 0.020%.

[0052] O: Oxygen in steel primarily exists as oxides. Excessive O content in steel indicates excessive oxides, potentially leading to the presence of large inclusions, which can affect the strength and toughness of the steel plate. Therefore, the present invention controls the O content to 0.0050% or less.

[0053] The surface microstructure of the substrate layer of the composite steel plate described in the present invention is 60-80% ferrite + 20-40% pearlite, and the central microstructure of the substrate layer is 30-40% pearlite + 60-70% ferrite. Since the working condition of the composite steel plate involved in the present invention is a maximum working temperature of 300°C, the strength and toughness properties required for the working condition can be met by controlling the microstructure type of the substrate layer of the composite steel plate to ferrite + pearlite. The pearlite content in the surface microstructure of the substrate layer is controlled to be 20-40%, slightly lower than the 30-40% ratio of the central microstructure. The purpose is to reduce the pearlite content in the surface microstructure while ensuring the basic mechanical properties of the material, so as to reduce the concentration of carbon at the surface, thereby reducing the carbon concentration difference between the materials on both sides of the transition layer and weakening the concentration barrier for the migration of carbon from the surface of the substrate layer to the transition layer.

[0054] The rolled composite steel plate of the present invention has a stable MC precipitate phase in the substrate layer, wherein M represents one or both of Nb and Ti, and the average major axis length of the MC precipitate phase is less than 600 nm. When the major axis length of the precipitate phase is large, it is easy to form a crack source for the initiation of microcracks inside the steel plate, thereby adversely affecting the mechanical properties of the steel plate. Therefore, it is necessary to control the average major axis length of the MC in the substrate layer to be less than 600 nm. In the substrate layer of the rolled composite steel plate of the present invention, as small a carbide precipitate phase as possible is formed to ensure that while fully exerting the carbon fixation effect of the carbide, the mechanical properties of the steel plate will not be adversely affected by the precipitation of the carbide. Therefore, the number ratio of the MC precipitate phase with a major axis length of less than 600 nm to the total MC precipitate phase is limited to greater than 50%.

[0055] The volume density of the MC precipitated phase with a major axis size of less than 600 nm in the substrate layer of the present invention is greater than 2.0×10 4 Pieces / mm 3 In order to prevent the free carbon from diffusing into the cladding material, the substrate steel plate of the present invention forms MC precipitates in the steel through composition and process control to fix the free carbon in the steel. Therefore, in the present invention, it is necessary to ensure that the volume density of the MC precipitates with a major axis size of less than 600 nm is greater than 2.0×10 4 Pieces / mm 3 , can effectively control the carbon element in the steel and avoid the large-scale diffusion of free carbon elements to the stainless steel side.

[0056] The composite steel plate cladding material of the present invention comprises 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. Larger carbide size in the cladding material significantly impacts the corrosion resistance of stainless steel. Therefore, it is desirable for the carbide precipitate phase in the cladding material to be as small as possible. However, during the production 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, the present invention requires that the average major axis length of the MC precipitate phase in the cladding material be less than 700 nm.

[0057] The volume density of the MC precipitated phase in the composite material of the present invention is less than 1.0×10 4 Pieces / mm 3 From the perspective of controlling the amount of carbide precipitation phase in the composite material, it is hoped that the amount of carbide is as small as possible, that is, the smaller the volume density is, the better. However, some carbides will inevitably form during the heat treatment of the composite steel plate. The volume density of the carbide is controlled to be less than 1.0×10 4 Pieces / mm 3 It can ensure the excellent corrosion resistance of the composite material.

[0058] In the composite material of the present invention, the MC precipitates with a major axis length of less than 700 nm account for greater than 50% of the total MC precipitates. In the present invention, the "volume density" of the MC precipitates is measured according to the method described in the YB / T5320-2006 standard. To minimize the carbide precipitates in the composite material and increase the corrosion resistance of the composite material, the present invention limits the size and number of the MC precipitates, namely, the MC precipitates with a major axis length of less than 700 nm account for greater than 50% of the total MC precipitates. When the number and size of the carbide precipitates exceed the limit, the corrosion resistance of the composite material will be greatly reduced, affecting the safe service performance of the rolled composite steel plate.

[0059] The cladding layer described in the present invention is made of stainless steel (including austenitic stainless steel, ferritic stainless steel, duplex stainless steel, and super stainless steel). The σ phase in its microstructure is an intermetallic phase with very high hardness and very low plasticity. When present in stainless steel, especially when precipitated along grain boundaries, it significantly affects the plasticity of the steel, leading to a significant reduction in its impact toughness. Therefore, the σ phase ratio in stainless steel is ≤ 1.5%, and in particular, the σ phase ratio near the bonding interface (transition layer) is ≤ 0.5%.

[0060] The present invention also provides a method for manufacturing the corrosion-resistant rolled composite steel plate, which comprises the following steps:

[0061] 1) Smelting and casting to obtain base material and composite casting billet

[0062] The above composition is smelted and cast to obtain a base material ingot; during the smelting process, deoxidizers Mn+Si, Al, and Ti alloys are sequentially added to the molten steel for deoxidation, and Mn+Si and Al are sequentially added for pre-deoxidation. After pre-deoxidation, the oxygen level of the molten steel is 0.0020% to 0.0075%, and then Ti is added for final deoxidation. After deoxidation, element B is added; after casting, a carbon steel base material ingot is obtained; and at the same time, stainless steel is produced or provided as a composite ingot.

[0063] 2) Assembly

[0064] After surface treatment, the base ingot and the composite ingot are laminated, the laminated ingot is sealed by welding around the edges, vacuumized, and sealed again to form a composite slab; preferably, the vacuum degree after vacuuming is 8 to 60 Pa;

[0065] 3) Composite slab rolling

[0066] The composite slab is heated to 1020-1200° C., and then rolled in two stages, wherein the total reduction ratio of the composite slab in the first stage is not less than 60% (e.g., 60-75%), the total reduction ratio of the composite slab in the second stage is not less than 20% (e.g., 20-30%), the reduction ratio of the last pass is 10-18%, and the total reduction ratio of the two stages rolling is not less than 80% (e.g., 80-97%), and the finishing rolling temperature is above 850° C. (e.g., 850-960° C.);

[0067] 4) Heat treatment: quenching and tempering the composite steel plate.

[0068] Preferably, in step 2), the surfaces of the substrate and the composite ingot are surface treated to ensure that there are no obvious oil stains, slag inclusions, cracks or other surface defects on the ingot surface, and the roughness of the processed ingot surface is no more than 2.0 Ra.

[0069] Preferably, in step 4), the quenching temperature is 920-955° C., the quenching holding time is T1=(1-1.2)H, and after the holding is completed, the product is taken out of the furnace and water-cooled to room temperature, wherein T1 is in min, and H is the thickness of the substrate layer in mm.

[0070] Preferably, in step 4), the tempering temperature is 550-700° C., and the tempering holding time T2 is (1-1.5) H, wherein T2 is in min, and H is the thickness of the substrate layer in mm.

[0071] In the manufacturing method of the present invention,

[0072] The composite steel plate substrate layer of the present invention requires the generation of a large amount of uniformly dispersed nano-scale MC precipitates. The MC precipitates are used to fix the free carbon in the carbon steel substrate layer, preventing the carbon from diffusing in large quantities to the interface between the substrate layer and the composite material, thereby preventing the formation of carbides in the stainless steel and reducing its corrosion resistance, thereby improving the service safety of the rolled composite steel plate for high-temperature equipment. However, free carbon in steel is a major strengthening element in the carbon steel substrate layer. When most of the free carbon is fixed in the form of MC, the strength of the carbon steel decreases. In order to compensate for the strength loss caused by the fixation of carbon, it is necessary to improve the hardenability of the steel plate by adding element B. The hardenability of element B is mainly affected by the distribution of free B at the grain boundaries. Since element B is an extremely active element, on the one hand, it can combine with oxygen in the molten steel to form boron oxide; on the other hand, element boron can easily combine with element N to form boron carbide.

[0073] To this end, the technical solution of the present invention specifically designs the deoxidation sequence of the molten steel and the timing of adding the element B. Specifically, during deoxidation, Si+Mn is first used for pre-deoxidation, causing the majority of silicon oxide and manganese oxide to float to the top slag. Deoxidation with the strong deoxidizer Al allows for relatively precise control of the oxygen level (measured according to the method for measuring oxygen content in molten steel as described in ISO 14284:1996) between 0.0020% and 0.0075%. Final deoxidation is then performed with Ti, forming a large amount of Ti oxide. The added Ti combines with free nitrogen in the steel to form TiN. The addition of Ti further reduces the free oxygen concentration in the steel. Within a certain oxygen level range (0.0020% to 0.0075%), the appropriately sized Ti2O3 inclusions formed after deoxidation (2-5 μm) facilitate the formation of a partial acicular ferrite structure during solidification and subsequent phase transformation, improving the toughness of the steel plate. Furthermore, Ti combines with nitrogen in the steel to form some TiN, which, on the one hand, 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, pinning the growth of austenite and refining the original austenite grains. Once the oxygen and titanium levels in the steel are properly controlled, an appropriate amount of B is added, ensuring that the added B is primarily present in the steel in a free state, ensuring that the base steel plate has high hardenability and significantly improving the strength of the steel plate.

[0074] In step 2), the surfaces of the substrate and composite slab are processed to ensure that the slab surface is free of obvious surface defects such as oil stains, slag inclusions, and cracks. The roughness of the processed slab surface is also required to be no greater than 2.0 Ra. After evacuation, the vacuum level is 8-60 Pa, which ensures the best rolling performance for the composite slab.

[0075] In step 3), the composite slab is heated to 1020-1200°C for rolling. This is because heating temperatures below 1020°C prevent the carbides and nitrides in the base cast from fully dissolving, reducing the carbides' pinning effect on the austenite grains during rolling. Furthermore, this temperature range facilitates homogenization of the austenite in the composite material and complete dissolution of the carbides in the composite material. However, heating the composite slab above 1200°C can lead to rapid growth of the austenite grains in the base and composite layers, compromising the mechanical properties of the steel.

[0076] Accordingly, it is preferred that the total reduction rate of the 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%, the reduction rate of the last pass is 8-18%, the total cumulative reduction rate of the two-stage rolling is not less than 80%, and the final rolling temperature is above 850°C.

[0077] Through the first stage of high-temperature and high-reduction rolling, the material can be fully recrystallized during the rolling deformation process, the austenite grains can be continuously refined, and the formation of larger austenite grains in the steel can be inhibited, 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 indicators of the steel plate.

[0078] The total reduction rate in the second stage of rolling is not less than 20%, which can further promote the refinement of austenite grains. The final rolling reduction rate is between 8% and 18%, which can increase the dislocation density in the steel and ensure the strength of the steel plate. The reduction rate is lower than 8%, and the dislocation density is low, which is not conducive to strength improvement. When the reduction rate is higher than 18%, the rolling torque is too large, which is not conducive to the rolling equipment. When the final rolling temperature is lower than 850℃, the deformation resistance of the steel plate increases, making it difficult to ensure a large final rolling reduction rate.

[0079] In step 4), the quenching temperature is 920-955°C, the quenching holding time is T1=(1-1.2)H, and after the holding is completed, the steel plate is taken out of the furnace and water-cooled to room temperature, wherein T1 is in min and H is the thickness of the steel plate in mm.

[0080] It should be noted that during the quenching process, when the quenching temperature is below 920°C, the steel's austenite homogenization takes a long time, reducing heat treatment efficiency. If the quenching temperature is above 955°C, some of the austenite in the carbon steel tends to grow, easily forming a mixed crystal structure, which is detrimental to the uniformity of the steel's structure. Accordingly, when the quenching and holding time T1 is less than 1 hour, the steel cannot fully austenitize. When the quenching and holding time T1 exceeds 1.2 hours, the steel exceeds the required austenitization time, which will reduce the efficiency of the quenching process.

[0081] In step 4), the tempering temperature is 550-700° C., and the tempering holding time T2 is (1-1.5) H, where T2 is in min and H is the thickness of the steel plate in mm.

[0082] During the tempering process, if the tempering temperature of the steel is below 550°C, a longer tempering time is required to remove residual quenching stresses in the steel, which reduces tempering efficiency and slows the formation of MC precipitates in the carbon steel. However, if the tempering temperature is above 700°C, the MC precipitates in the steel are prone to Ostwald coarsening and aggregation, which is not conducive to the formation of fine, dispersed MC precipitates in the steel. Accordingly, if the tempering holding time T2 is less than 1.0 h, the quenching stresses in the steel tend not to be completely removed. If the tempering holding time T2 is greater than 1.5 h, the MC precipitates in the steel tend to coarsen, reducing the production efficiency of the tempering process.

[0083] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0084] 1. The present invention utilizes fine, dispersed spherical (2-5 μm) Ti2O3 oxides formed in the steel to serve as nucleation cores for MC carbide precipitation. 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) precipitation phases can be formed in the substrate layer. This can immobilize free carbon in the substrate layer, reduce the diffusion and aggregation of carbon at the composite interface, reduce the precipitation of carbides at the stainless steel grain boundaries, and ensure the corrosion resistance of the composite rolled steel plate. In particular, when the rolled composite steel plate is used in high-temperature equipment, even under high-temperature conditions of 300°C, the high-melting-point Ti2O3 oxides (melting point of 2130°C) formed by the controlled smelting process can remain stably present in the steel, serving as precipitation cores for MC carbides and continuing to function. That is, some of the free carbon elements in the steel can still react with the alloying elements in the steel with Ti2O3 oxide as the nucleation core to form fine MC carbides, thereby further fixing the carbon elements, ensuring that the carbon elements in the carbon steel do not diffuse to the interface, and protecting the corrosion resistance of the rolled composite steel plate under long-term high-temperature service.

[0085] 2. In the current production process of low-alloy, high-strength steel, aluminum is often used as a deoxidizer to minimize the oxygen content in the steel. While aluminum deoxidation offers the advantage of high deoxidation efficiency, its disadvantage is that Al2O3 inclusions formed in the molten steel can adversely affect the flaw detection and performance of the steel plate. This is primarily because individual Al2O3 inclusions are often irregular and sharp, easily initiating cracks within the material when the substrate layer is subjected to stress. Furthermore, Al2O3 inclusions easily aggregate and grow in the molten steel, forming large Al2O3 clusters that can block the pouring nozzle. Furthermore, the presence of large inclusions in steel can easily cause fluctuations in the tensile and impact properties of the steel plate. Furthermore, Al2O3 inclusions cannot serve as nucleation sites for carbide precipitation.

[0086] In the present invention, by controlling the type, sequence, and amount of deoxidizer added during the steelmaking process, a fine, dispersed, spherical (2-5 μm) Ti2O3 oxide with a high melting point is ultimately formed in the steel. The Ti2O3 oxide is less likely to aggregate and grow in the molten steel, is inherently flat, and does not significantly impair the flaw detection and mechanical properties of the steel plate, thereby optimizing the steel plate's microstructure. By controlling the element content ratio, TiN precipitation is controlled, refining the austenite grains. By designing the order of addition of the steel alloy, the amount of oxidation and nitridation of the boron element can be effectively reduced, thereby maximizing the utilization of the added boron element, maximizing the hardenability of the steel plate, refining the grains, and ensuring the steel plate has high strength and excellent low-temperature toughness.

[0087] Furthermore, through smelting process control, particularly by controlling the type, sequence, and amount of deoxidizers added, the fine, dispersed spherical (2-5 μm) Ti2O3 oxides formed in the steel can serve as nucleation cores for the precipitation of MC carbides. 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 layer. These can immobilize free carbon in the substrate layer, reduce the diffusion and aggregation of carbon at the composite interface, and reduce the precipitation of carbides at the grain boundaries of the stainless steel, thereby ensuring the corrosion resistance of the composite rolled steel plate. In particular, when the rolled composite steel plate is used in high-temperature equipment, even under high-temperature conditions of 300°C, the high-melting-point Ti2O3 oxides (melting point 2130°C) formed by the controlled smelting process can remain stable in the steel, serving as precipitation cores for MC carbides and continuing to function. That is, some of the free carbon elements in the steel can still react with the alloying elements in the steel with Ti2O3 oxide as the nucleation core to form fine MC carbides, thereby further fixing the carbon elements, ensuring that the carbon elements in the carbon steel do not diffuse to the interface, and protecting the corrosion resistance of the rolled composite steel plate under long-term high-temperature service.

[0088] The composite steel plate produced by the present invention has excellent corrosion resistance and can be effectively used in the energy and chemical industry as a manufacturing material for reaction vessels at room temperature to 300°C. It has very important practical significance and a very broad application prospect. DETAILED DESCRIPTION

[0089] The rolled composite steel plate for high-temperature equipment and the manufacturing method thereof according to the present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an undue limitation to the technical solution of the present invention.

[0090] The compositions of the base material and cladding layer of the rolled composite steel plates in the Examples and Comparative Examples of the present invention are shown in Table 1, with the remainder comprising Fe and other unavoidable impurities. Austenitic stainless steel is used as the cladding material for the rolled composite steel plates in the Examples and Comparative Examples. The manufacturing process parameters for the Examples of the present invention are shown in Table 2. Commercially available austenitic stainless steel can be used as the cladding slab.

[0091] The manufacturing method of the embodiment of the present invention comprises the following steps:

[0092] 1) Smelting and casting: Smelting and continuous casting are carried out according to the chemical composition shown in Table 1 to produce ingots. The smelting equipment uses a 500 kg vacuum induction furnace. First, 410 kg 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 evacuated and smelting is carried out at a minimum vacuum degree of about 25 Pa. Argon gas is required for atmosphere protection during the smelting process; after the pure iron is melted, deoxidizers Si+Mn and Al are added in sequence for pre-deoxidation. According to the online monitoring results of the molten steel composition, the amount of deoxidizer added is fine-tuned and the oxygen level of free oxygen in the molten steel is controlled to 0.0020-0.0075%. Then, an appropriate amount of Ti is added for final deoxidation; alloys such as Nb are added for alloying treatment, and finally B is added. The ingots are cast using the top-pouring method;

[0093] 2) Assembling, the base carbon steel slab and the clad stainless steel slab are processed and the surface roughness 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, cracks, etc. After welding around the slab, vacuum is drawn to a vacuum degree of 8-60Pa;

[0094] 3) rolling, heating the composite slab at 1020-1200° C., and then performing two-stage rolling, with the total cumulative reduction ratio of the rolling being not less than 80%, and the final rolling temperature being above 850° C.;

[0095] 4) heat treatment, quenching and tempering the rolled composite steel plate; quenching the composite rolled steel plate at a quenching temperature of 920-955° C. for a quenching holding time T1 of (1-1.2) hours, and cooling the plate to room temperature after removal from the furnace with water; then tempering the plate at a tempering temperature of 550-700° C. for a tempering holding time T2 of (1-1.5) hours, and cooling the plate to air after removal from the furnace; wherein T1 and T2 are in minutes, and H is the thickness of the substrate layer in mm.

[0096] In the present invention, the chemical composition design and related processes of the clad steel plates of Examples 1 to 7 all meet the design specification requirements of the present invention.

[0097] Accordingly, the composite steel plates of Comparative Examples 1 to 5 are manufactured using the same process steps as Examples 1 to 7, with the following differences: the alloy element content of the carbon steel in the base layer of Comparative Examples 1 to 4 exceeds the design range, while the element content in Comparative Example 5 is within the design range; however, in the smelting and casting operations of the above step 1), the order of adding the deoxidizer and the B alloy in Comparative Examples 1 to 5 is different; and the heat treatment and tempering processes are different.

[0098] Electrolytic samples were taken from the base material and the stainless steel side of the composite layer at the interface of each composite steel plate from Examples 1 to 7 and the control composite steel plates from Comparative Examples 1 to 5. MC precipitates were extracted from the stainless steel using electrolytic extraction, and precipitates of varying size ranges were separated using filter membranes of varying particle sizes. The particle size distribution of the precipitates was determined using a laser particle size analyzer, and image analysis software was used to determine the quantity and size distribution of the MC precipitates (M represents one or more of Nb, Ti, Cr, and Mo) in the steel plates from each Example and Comparative Example. The data obtained from these observations and analyses are summarized in Table 3 (base material) and Table 4 (composite material at the interface, i.e., transition layer).

[0099] As shown in Table 3, the total number of precipitated phases in the composite steel plate substrate layer materials of Examples 1 to 7 ranges from 516 to 594, which is much higher than the 297 to 319 in the substrate layer materials of Comparative Examples 1 to 5. This indicates that after the implementation of the technical solution of the present invention, a larger number of MC carbide precipitates can be formed in the substrate layer material, thereby ensuring the effect of fixing the free carbon in the carbon steel by the stable carbides in the substrate layer as designed in the technical solution. Moreover, the size of the MC precipitates in the composite steel plate substrate layer materials of Examples 1 to 7 is relatively small, and their main distribution range is 300 to 600 nm. The average major axis length of the MC precipitates is less than 600 nm, and the volume density of the MC precipitates is greater than 2.0×10 4 Pieces / mm 3. The number ratio of MC precipitates with a size of less than 600nm to the total MC precipitates is greater than 50%. When the size of the precipitates is small, it can play a role in pinning the growth of austenite grains to a certain extent, thereby refining the grains and further improving the strength and toughness of the material. In contrast, the size of the MC precipitates in the carbon steel of the substrate layer of the rolled composite steel plates in Comparative Examples 1 to 5 is relatively large, the average major axis length of the MC precipitates is greater than 800nm, the size distribution range of the main precipitates is above 800nm, and the proportion of precipitates with a size of more than 1000nm is relatively high, which has a poor pinning effect on the austenite grains, resulting in a larger grain size and affecting the strength and toughness of the steel plate. Since the number of stable precipitates formed in the carbon steel material of the comparative example 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 being segregated to the bonding interface, thereby generating a large amount of carbides precipitated at the grain boundaries in the composite material at the bonding interface, reducing the corrosion resistance of the composite material at the bonding interface.

[0100] As shown in Table 4, in the composite steel plate cladding materials of Examples 1 to 7, the number of MC precipitates detected is 182 to 244, which is much less than 424 to 506 in the comparative example. Moreover, the volume density of the MC precipitates in the cladding materials at the transition layer of the examples is less than 1×10 4 Pieces / mm 3 . This shows that the amount of carbon in the carbon steel material of the base layer of Examples 1 to 7 that diffuses into the cladding material through the bonding interface (transition layer) is small, and the amount of MC formed is small, while in Comparative Examples 1 to 5, a large amount of carbon elements in the carbon steel material diffuses into the cladding material through the bonding interface, resulting in a larger amount of carbides in the corresponding cladding materials. At the same time, it can be seen from Table 4 that in the cladding materials at the bonding interface of Examples 1 to 7, the average major axis length of the MC precipitate phase is less than 700nm, and the MC precipitate phase with a size less than 700nm accounts for more than 50% of the total MC precipitate phase; correspondingly, the average size of the MC precipitate phase obtained by inspection in the comparative example is greater than 850nm. This further illustrates that the carbide fixing effect on free carbon in the examples is much better than that in the comparative example.

[0101] After analyzing the carbide precipitation phases of 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 carbon steel substrate layer of the comparative example are lower than those of the examples. This is mainly due to the fact that the smelting process, alloy addition sequence, and heat treatment process of the carbon steel in the comparative example substrate layer are different from those in the examples. As a result, the hardenability of the B element in the comparative example steel cannot be fully exerted. In addition, the different precipitation phases in the steel have different effects on the microstructure of the steel plate. In the substrate layer of the composite steel plate of the present invention, the surface microstructure is 60-80% ferrite (F) and 20-40% pearlite (P), while the core microstructure of the substrate layer is 30-40% pearlite and 60-70% ferrite. The smaller precipitated phases in the embodiment further refine the austenite grains, which plays a certain role in improving the strength and toughness of the steel plate.

[0102] Intergranular corrosion testing was performed on the stainless steel at the interface of the rolled composite steel plates from the examples and comparative examples according to ASTM A262 Practice E. The test results are shown in Table 6. These results demonstrate that the stainless steel at the interface of the rolled composite steel plates produced according to the technical requirements of the present invention exhibits excellent corrosion resistance. Therefore, the corrosion resistance of the composite stainless steel plates of Examples 1-7 is significantly superior to that of the comparative examples.

[0103] In summary, the composite steel plate of the present invention, by optimizing the design and production process, controlling the type of deoxidizer, deoxidation sequence, and amount of deoxidizer added during the steel smelting process, performing alloying treatment in a certain order, and coordinating with a specific production process, can generate a large number of dispersed nano-scale MC (M represents one or both of Nb and Ti) precipitates in the steel. These nano-scale MC precipitates can fix the free carbon elements in the carbon steel of the substrate, thereby preventing these carbon elements from diffusing in large quantities to the bonding interface, resulting in the formation of a large number of carbide precipitates in the stainless steel, which reduces the corrosion resistance of the stainless steel. Therefore, the use of the technical solution of the present invention can ensure the strength and toughness of the carbon steel substrate, 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 service at high temperatures.

[0104] In addition, it should be noted that the combination of the various technical features in the present invention is not limited to the combination described in the claims of the present invention or the combination described in the specific embodiments. All technical features described in the present invention can be freely combined or combined in any way unless there is a contradiction between them.

[0105] 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 therefrom that can be directly derived from or easily conceived by those skilled in the art based on the disclosure of the present invention are intended to fall within the scope of protection of the present invention.

[0106] Table 6

Claims

1. A corrosion-resistant rolled composite steel plate, which is rolled by composite rolling of carbon steel as a substrate and stainless steel as a composite layer, comprising a substrate layer, a composite layer and a transition layer between the substrate layer and the composite layer, wherein: The composition weight percentage of the substrate layer is: C: 0.01% to 0.10%, Si: 0.20% to 0.70%, Mn: 0.30% to 1.70%, Ti: 0.006% to 0.012%, Als: 0.008% to 0.018%, Nb: 0.0090% to 0.050%, B: 0.0010% to 0.0050%, N: 0.0015% to 0.0050%, P≤0.017%, S≤0.020%, O≤0.0050%, and the balance includes Fe and other inevitable impurities; The surface microstructure of the substrate layer is 60-80% ferrite + 20-40% pearlite + MC precipitation phase in area percentage, and the central microstructure of the substrate layer is 30-40% pearlite + 60-70% ferrite + MC precipitation phase in area percentage; wherein M represents one or both of Nb and Ti, the average major axis length of the MC precipitation phase is less than 600nm, and the volume density of the MC precipitation phase with a major axis length less than 600nm is greater than 2.0×10 4 Pieces / mm 3 ; The microstructure of the composite layer contains MC precipitated phase, wherein M represents one or more of Cr, Mo, Nb, and Ti, the average major axis length of the MC precipitated phase is less than 700 nm, and the volume density of the MC precipitated phase is less than 1.0×10 4 Pieces / mm 3 .

2. The corrosion-resistant rolled composite steel plate according to claim 1, 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%, 0<Cu≤0.55%.

3. The corrosion-resistant rolled composite steel plate according to claim 1 or 2, characterized in that: The balance of the composite steel plate base material is Fe and other inevitable impurities.

4. The corrosion-resistant rolled composite steel plate according to claim 1, 2 or 3, characterized in that: In the composite steel plate substrate layer, the MC precipitated phases with a major axis length of less than 600 nm account for more than 50% of the total MC precipitated phases.

5. The corrosion-resistant rolled composite steel plate according to claim 1, 2, 3 or 4, characterized in that: The stainless steel is selected from austenitic stainless steel, ferritic stainless steel, duplex stainless steel and super stainless steel.

6. The corrosion-resistant rolled composite steel plate according to any one of claims 1 to 4, characterized in that: The weight percentage of the components of the stainless steel is: C: 0.01-0.05%; Si: 0.50-0.80%; Mn: 1.10-1.50%; Ni: 6.5-9.5%; Cr: 15.0-22.0%; N: 0.060~0.120%; P: ≤0.015%; S: ≤0.005%; O: ≤0.005%; the balance is Fe and other inevitable impurities.

7. The corrosion-resistant rolled composite steel plate according to any one of claims 1 to 6, characterized in that: In the multi-layer, the MC precipitated phase with a major axis length less than 700 nm accounts for more than 50% of the total MC precipitated phase.

8. The corrosion-resistant rolled composite steel plate according to any one of claims 1 to 7, characterized in that: The microstructure of the composite steel plate layer also contains a σ phase with an area ratio of ≤1.5%. Preferably, the area ratio of the σ phase close to the transition layer is ≤0.5%.

9. The corrosion-resistant rolled composite steel plate according to any one of claims 1 to 8, characterized in that: The thickness of the composite steel plate substrate is ≥6 mm, and the thickness of the composite layer is ≥2 mm; preferably, the thickness of the transition layer is ≤230 μm; preferably, the thickness of the substrate layer is 6 to 200 mm, 10 to 200 mm or 10 to 100 mm; preferably, the thickness of the composite layer is 2 to 20 mm; preferably, the thickness of the transition layer is 1 to 230 μm, 1 to 150 μm or 1 to 50 μm.

10. The corrosion-resistant rolled composite steel plate according to any one of claims 1 to 9, characterized in that: The yield strength of the substrate layer is ≥255MPa, the tensile strength is ≥390MPa, the cross-sectional shrinkage is ≥60%, the elongation is ≥20%, the -20°C impact absorption energy is ≥200J, and the -40°C impact absorption capacity is ≥120J; the substrate grain size grade is not less than grade 6.0; the shear strength of the composite steel plate is ≥280MPa.

11. The corrosion-resistant rolled composite steel plate according to claim 10, characterized in that: The yield strength of the base material layer of the composite steel plate is ≥280MPa or ≥300MPa, or between 255 and 400MPa or between 280 and 400MPa; The tensile strength of the base material layer of the composite steel plate is ≥410MPa or ≥430MPa, or between 390 and 500MPa or between 410 and 500MPa; The cross-sectional shrinkage of the base material layer of the composite steel plate is ≥70%, or between 60% and 80% or between 70% and 80%; The elongation of the base material layer of the composite steel plate is ≥23%, or between 20% and 27%, or between 23% and 27%; The -20°C impact absorption energy of the base material layer of the composite steel plate is ≥230J, or between 200 and 260J or between 230 and 260J; The -40°C impact absorption energy of the base material layer of the composite steel plate is between 120 and 150 J; The shear strength at the composite interface of the base material layer of the composite steel plate is ≥300 MPa, or between 280 and 360 MPa.

12. The method for manufacturing a corrosion-resistant rolled composite steel plate according to any one of claims 1 to 11, characterized in that: The steps include: 1) Smelting and casting to obtain base material casting billet The base material ingot is obtained by smelting and casting the composition according to claim 1, 2 or 3; during the smelting process, firstly First, Mn+Si and Al are added for pre-deoxidation, and the oxygen level of the molten steel after pre-deoxidation is 0.0020% to 0.0075%, and then Ti is added for final deoxidation; after deoxidation, B element is added; after casting, the base material ingot is obtained; Preparing or providing stainless steel as a composite casting slab; 2) Assembly The substrate casting blank and the composite casting blank are overlapped after surface treatment, and the overlapping casting blank is welded and sealed around, vacuumized, and sealed again to form a composite slab; preferably, the vacuum degree after vacuuming is 8-60Pa; 3) Composite slab rolling The composite slab is heated to 1020-1200°C, and then rolled in two stages, the total reduction rate of the composite slab in the first stage is not less than 60%, the total reduction rate in the second stage is not less than 20%, the reduction rate of the last pass is 8-18%, the total reduction rate of the two-stage rolling is not less than 80%, and the final rolling temperature is above 850°C; 4) Heat treatment: quenching and tempering the composite steel plate.

13. The method for manufacturing a corrosion-resistant rolled composite steel plate according to claim 12, wherein: In step 2), the surfaces of the substrate and the composite ingot are treated to ensure that there are no obvious oil stains, slag inclusions, cracks or other surface defects on the ingot surface, and the roughness of the ingot surface is not greater than 2.0 Ra.

14. The method for manufacturing a corrosion-resistant rolled composite steel plate according to claim 12, wherein: In step 4), the quenching temperature is 920-955°C, the quenching holding time is T1=(1-1.2)H, and after the holding time is completed, the product is taken out of the furnace and cooled to room temperature with water, wherein T1 is in min, and H is the thickness of the substrate layer in mm.

15. The method for manufacturing a corrosion-resistant rolled composite steel plate according to any one of claims 12 to 14, characterized in that: In step 4), the tempering temperature is 550-700° C., and the tempering holding time T2=(1-1.5)H, wherein T2 is in min, and H is the thickness of the substrate layer in mm.

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