Composite board and manufacturing method thereof

Abstract

A composite plate (1) comprising an iron-based alloy layer (3) formed from an iron-based alloy, and nickel-containing layers (2, 4) laminated on one or both surfaces of the iron-based alloy layer and having Ni as the main component, the total thickness of the composite plate being greater than 0.1 mm and 3.0 mm or less, and the thickness of the nickel-containing layers (2, 4) being between at least one surface of the iron-based alloy layer and the nickel-containing layers (2, 4). A diffusion layer having a Ni concentration and a Fe concentration of 10 mass% or more is present at an average thickness of 0.50 [mu] m or more and 10.0 [mu] m or less, and the number density of granular Al-enriched portions having an Al concentration of 15 mass% or more and an equivalent circle diameter of 250 nm or more is less than 0.50 / [mu] m2 in a cross-section including the diffusion layer and having a direction perpendicular to the rolling direction and the sheet thickness direction as a normal.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a clad plate and a manufacturing method thereof. BACKGROUND

[0002] Nickel exhibits high corrosion resistance in an environment immersed in an alkaline solution. Therefore, it is used for, for example, cathode materials, pad materials, and the like of a salt electrolysis device used in the production of caustic soda, which is a basic industrial chemical, and the like, which are resistant to alkaline corrosion.

[0003] In recent years, in order to suppress climate change caused by greenhouse gases typified by carbon dioxide, technologies for realizing a carbon-neutral society have attracted attention. In particular, nickel used for electrode materials of secondary batteries used in various electrification technologies typified by electric vehicles and the like, electrodes of alkaline water electrolysis devices, pad materials, and the like are expected to increase in demand for utilizing hydrogen energy in the future. Nickel materials used in these uses are using a plate material formed of a single pure nickel metal.

[0004] On the other hand, nickel metal is expensive, and furthermore, there is a tendency for raw material metal prices to easily fluctuate due to changes in the global supply and demand balance of nickel ores. In the future, in order to realize the aforementioned carbon-neutral society, the demand for nickel is expected to increase dramatically.

[0005] As described above, nickel has extremely high corrosion resistance in an alkaline environment. Therefore, thinning in the use of nickel in an alkaline environment is not likely to be a problem. Therefore, by using a commonly used and inexpensive metal material for the inner layer portion and using a plate material provided with nickel for the outer layer, it is possible to reduce the cost spent on the blank.

[0006] As a method of manufacturing such a multi-layered plate material, for example, there is a method of performing nickel plating on the surface of a carbon steel, which is a commonly used metal. Patent Literature 1 discloses a high corrosion-resistant nickel-plated steel strip in which a nickel-plated layer is formed on one side or both sides of a carbon steel plate, and part or all of the nickel-plated layer forms a nickel-iron diffusion layer, and the exposure ratio of iron at the surface of the aforementioned nickel-plated layer is 30% or less. Such nickel plating can form a nickel-plated layer by electroplating or chemical plating using a catalyst, and heat treatment and the like after plating are performed as needed.

[0007] A multi-layered material based on such plating can suppress the amount of nickel used, but on the other hand, there is a risk that iron will be exposed at a bending process portion when used in a factory or the like. Therefore, there is a need for a multi-layered material having a nickel layer with a thickness of the thickness or more that can be achieved by plating.

[0008] As an example of a multi-layered steel plate other than plating, there is a clad material in which a partner material for imparting a new function is joined to the surface of a base material formed of a commonly used metal.

[0009] For example, Patent Literature 2 discloses a method of overlapping a set of clad materials formed of carbon steel as a base material and one of stainless steel, pure nickel, and nickel alloy, and welding a peripheral portion, and hot-rolling the resulting assembled material to obtain a clad plate. In the example of Patent Literature 2, a clad steel plate having a rolling end thickness of 30 mm was manufactured.

[0010] Patent Literature 1: Japanese Patent Application Laid-Open No. H6-2104

[0011] Patent Literature 2: Japanese Patent Application Laid-Open No. H1-192404 SUMMARY

[0012] Problem to be solved by the invention

[0013] The nickel clad plate disclosed in Patent Literature 2 and the nickel clad plate prescribed in JIS G 3602:2012 are thick, and in particular, the nickel clad plate prescribed in JIS is prescribed only as 1 mm or more and less than 5 mm, or 5 mm or more in terms of the thickness of the outer layer nickel of the clad material.

[0014] A nickel metal member for an electrolytic device used in an alkaline environment, which is in high demand at present, is preferably a plate having a thickness of 3 mm or less from the viewpoint of reducing the cost of a raw material. Therefore, the thickness of the nickel-containing layer of a nickel clad plate as a substitute therefor, and also the thickness of the clad plate itself, are also preferably minimized.

[0015] As disclosed in Patent Literature 2, Fe-Ni cladding of thick plates has been put into practical use. On the other hand, Fe-Ni cladding of thin plates having a thickness of 3 mm or less has not been known to date. For thin plates, a manufacturing process such as cold rolling, which is difficult to apply to thick plates, can be used to manufacture thin plates having a total thickness of the plate adjusted with good accuracy, but on the other hand, it is generally required to have a bending workability that forms a larger angle compared to thick plates.

[0016] For example, in the case of using a carbon steel as a base material, a nickel as a clad material, laminating them and performing rolling or press joining, and using the clad thin plate joined by mutual diffusion as a substitute for an existing nickel single thin plate, peeling of the layer interface at the bending work portion, and exposure of the base material due to breakage of the clad material, and the like become problems. The clad plate is different from a single material, and there is an interface of nickel and carbon steel (hereinafter referred to as a dissimilar metal interface) inside the plate. Nickel and carbon steel are different in mechanical properties and deformation behavior, and furthermore, the dissimilar metal interface itself also has different mechanical properties. Therefore, a clad plate in which a clad material having nickel as a main component and an iron-based alloy such as carbon steel as a base material is not easy to cause interface peeling with the dissimilar metal interface as a boundary in bending work to a certain extent or more, and it is preferable that a material in which exposure of the core material due to breakage of the clad material is further less likely to occur be developed.

[0017] The present disclosure has been made in view of the above problems. That is, the present disclosure is to provide a clad plate in which interfacial peeling of a nickel-containing layer mainly composed of Ni and an iron-based alloy layer does not easily occur even if bending processing is performed.

[0018] Means for solving the problem

[0019] The above problems can be solved by the following means.

[0020] [1] A clad plate comprising an iron-based alloy layer formed of an iron-based alloy, and a nickel-containing layer mainly composed of Ni laminated on at least one side of the aforementioned iron-based alloy layer,

[0021] The total thickness of the clad plate is greater than 0.1 mm and is 3.0 mm or less,

[0022] Between at least one side of the aforementioned iron-based alloy layer and the aforementioned nickel-containing layer, a diffusion layer in which each of the concentrations of Ni and Fe is 10 mass% or more is present at an average thickness of 0.50 μm or more and 10.0 μm or less, and within the aforementioned diffusion layer including the aforementioned diffusion layer and in a section having a normal in a direction perpendicular to a rolling direction and a plate thickness direction, the number density of granular Al-rich portions in which the concentration of Al is 15 mass% or more and the equivalent circle diameter is 250 nm or more is less than 0.50 pieces / μm 2 .

[0023] [2] The clad plate according to [1], wherein the aforementioned nickel-containing layer is laminated on both sides of the aforementioned iron-based alloy layer, the aforementioned diffusion layer is present between each of both sides of the aforementioned iron-based alloy layer and the aforementioned nickel-containing layer, and within each of the aforementioned diffusion layers in the aforementioned section, the number density of the aforementioned granular Al-rich portions is less than 0.50 pieces / μm 2 .

[0024] [3] The clad plate according to [1] or [2], wherein the thickness of the aforementioned nickel-containing layer is 30 μm or more and 300 μm or less.

[0025] [4] A manufacturing method of a clad plate according to any one of [1] to [3], the manufacturing method comprising the following steps:

[0026] a lamination step of laminating in a state in which an Fe-Ni alloy foil having a thickness of 0.050 mm or more and 0.125 mm or less, containing 35.0 to 65.0 mass% of Ni, 0.50 mass% or less of Al, and the balance being Fe and impurities, is disposed between a slab or an iron-based alloy material as a thick plate on one side or both sides of an iron-based alloy slab or an iron-based alloy material as a thick plate, and a slab or a nickel-containing material as a thick plate, and welding the periphery portion including the lengthwise end portion and the widthwise end portion to make a closed laminate;

[0027] a rolling joining process of joining the aforementioned iron-based alloy blank and the aforementioned nickel-containing blank by hot-rolling the aforementioned laminate to produce a joined body;

[0028] a cold-rolling process of cold-rolling the aforementioned joined body to produce a clad plate; and

[0029] an annealing process of annealing the clad plate after the aforementioned cold-rolling process with an annealing temperature T (°C) and an annealing time t (s) set to satisfy the following equation (1).

[0030] 0.010 ≤ 0.2958 × A × R × [0.001 × t × exp{-8596.1 / (T+273.15)}] 1 / 2 ≤ 0.200 (1)

[0031] In the aforementioned equation (1), A (mm) is the thickness of the aforementioned Fe-Ni alloy foil, and R (%) is a rolling rate from a state of the laminate before the aforementioned rolling joining process to the clad plate after the aforementioned cold-rolling process, and is calculated from the following equation (2).

[0032] R (%) = 100 × (X - W) / X (2)

[0033] In the aforementioned equation (2), X (mm) is the thickness of the laminate before the rolling joining process, and W (mm) is the thickness of the clad plate after the aforementioned cold-rolling process.

[0034] Effects of the invention

[0035] According to the present disclosure, a clad plate in which interfacial peeling of a nickel-containing layer mainly composed of Ni and an iron-based alloy layer does not easily occur even when bending processing is performed is provided. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is an explanatory diagram showing the overall configuration of an example of the clad plate of the present disclosure.

[0037] Figure 2 is a diagram schematically showing the distribution of the composition of elements in a diffusion layer present in the vicinity of the dissimilar metal interface of the clad plate of the present disclosure. DETAILED DESCRIPTION

[0038] An embodiment as an example of the present disclosure will be described.

[0039] Note that, in the present disclosure, the range of values indicated using "~" means a range including the values written before and after the "~" as lower limit values and upper limit values. However, the range of values when the values written before and after the "~" are indicated as "greater than" or "less than" means a range excluding these values as lower limit values or upper limit values.

[0040] The "%" with respect to the content of elements of the chemical composition means "mass %".

[0041] The content of elements of the chemical composition is described as "0~" means that the element can not be contained.

[0042] The term "process" does not only mean an independent process, but also includes a process as long as the desired purpose of the process can be achieved even if it cannot be clearly distinguished from other processes.

[0043] The present inventors have conducted intensive studies in order to solve the above problems, and as a result, have obtained the following recognition.

[0044] (A) A clad plate of nickel and carbon steel joined by a hot rolling method is a layer (hereinafter referred to as a diffusion layer) in which the elements of each other exist near the dissimilar metal interface as a result of diffusion. The diffusion layer is a layer that is inevitably formed when the base material layers of each layer are stacked and joined by hot rolling or hot press joining, or the like. When the plate subjected to the hot joining is processed into a thin plate by cold working such as cold rolling, the diffusion layer does not disappear.

[0045] (B) When bending processing is performed, in the case where the thickness of the diffusion layer is below a certain level, a slight gap can sometimes occur at the dissimilar metal interface. In addition, even if the thickness of the diffusion layer is made to be above a certain level by heat treatment or the like, a gap can also sometimes occur at the interface due to bending processing.

[0046] (C) Furthermore, in the diffusion layer, there can be a region in which Al having a granular morphology is enriched (hereinafter referred to as an Al enriched portion), which is believed to originate from Al that is inevitably contained in nickel and carbon steel as a refining element or an impurity.

[0047] (D) In the case where the diffusion layer contains an Al enriched portion having a diameter of a certain level or more in an amount of a certain level or more, when bending processing is performed, a slight gap can occur between the nickel-containing layer and the carbon steel layer, or peeling can occur.

[0048] (E) If a nickel / carbon steel interface having a diffusion layer thickness within a certain range and an Al enriched portion having a granular morphology with a diameter of a certain level or more does not exist or exists in a small amount even if it exists, then interface peeling when bending processing is performed is less likely to occur.

[0049] (F) If the thickness of the nickel-containing layer as a partner material is below a certain level, in the case where the nickel-containing layer is present at the outer peripheral portion of the clad plate (a face on the outer side of the bending processed portion) in the bending processing of the clad plate, the nickel-containing layer can break and the carbon steel as a base material can be exposed.

[0050] The clad plate of the present disclosure was created based on the above recognition.

[0051] [Composite sheet]

[0052] (1) Overall configuration

[0053] The composite sheet of the present disclosure includes an iron-based alloy layer formed of an iron-based alloy, and a nickel-containing layer laminated on at least one side of the iron-based alloy layer and containing Ni as a main component. The total thickness of the composite sheet of the present disclosure is greater than 0.1 mm and is 3.0 mm or less. Between at least one side of the iron-based alloy layer and the nickel-containing layer, a diffusion layer in which each of the concentrations of Ni and Fe is 10 mass% or more is present at an average thickness of 0.50 pm or more and 10.0 pm or less. Also, in the diffusion layer in a section including the diffusion layer, which is a normal line in a direction perpendicular to the rolling direction and the sheet thickness direction, the number density of granular Al-rich portions in which the concentration of Al is 15 mass% or more and the equivalent circle diameter is 250 nm or more is less than 0.50 pieces / pm 2 .

[0054] The composite sheet of the present disclosure can be a two-layer composite sheet in which one iron-based alloy layer and one nickel-containing layer are laminated, or a three-layer composite sheet in which an iron-based alloy layer is laminated between two nickel-containing layers. In the case of a three-layer composite sheet, diffusion layers are present at two interfaces between the nickel-containing layers and the iron-based alloy layer, and one diffusion layer or both diffusion layers can satisfy the above conditions. From the perspective of suppressing interfacial peeling regardless of the bending direction of the composite sheet, it is preferable that both diffusion layers satisfy the above conditions.

[0055] Hereinafter, as an example of the composite sheet of the present disclosure, a three-layer composite sheet in which a nickel-containing layer, an iron-based alloy layer, and a nickel-containing layer are sequentially laminated will be mainly described with reference to the drawings. Note that in the following description, the symbols in the drawings will be appropriately omitted. In addition, sometimes, as a preferred mode, a layer formed of pure nickel will be described as a nickel-containing layer, and a layer formed of carbon steel will be described as an iron-based alloy layer.

[0056] Figure 1 is an explanatory view showing the overall configuration of an example of the composite sheet of the present disclosure. As shown in Figure 1 , the composite sheet 1 has a first layer 2, a second layer 3, and a third layer 4. The second layer 3 is an iron-based alloy layer containing Fe as a main component, and the first layer 2 and the third layer 4 are nickel-containing layers containing Ni as a main component. In the present disclosure, the "main component" of a layer refers to the element having the largest content (mass%) among the elements constituting the layer.

[0057] The second layer 3 is joined to the first layer 2 by one of the front and back surfaces (both surfaces). The second layer 3 is joined to the third layer 4 by the other of the front and back surfaces (both surfaces).

[0058] At the interface between the first layer 2 and the second layer 3, and the interface between the second layer 3 and the third layer 4 of the composite plate of the present disclosure, a diffusion layer in which Ni and Fe, which are the main constituent elements of each layer, are mixed together by diffusion exists in a certain thickness. Inside the diffusion layer, an Al-rich portion is likely to be formed, which is believed to be formed from Al mixed in as an element for refining, or an impurity, in nickel and carbon steel, and in the composite plate of the present disclosure, there is no Al-rich portion having an equivalent circle diameter of 250 nm or more in the diffusion layer, or even if there is one, it is in a small amount.

[0059] (2) First layer and third layer (nickel-containing layer)

[0060] The first layer and the third layer are nickel-containing layers in which Ni is the main component (for example, 50% or more), and are preferably composed of pure nickel.

[0061] Regarding pure nickel, which can be suitably used as a material for manufacturing the composite plate of the present disclosure, as its elemental composition, it is preferable to contain 98% or more of Ni in terms of mass%, and more preferably the content of Ni is 99% or more. The balance is impurities mixed from the main raw material or used in the refining process. Impurity elements can be exemplified by C, O, N, B, Si, P, S, Al, Ti, Nb, Mo, Mg, Ca, Mn, Cr, Co, Cu, Fe, and the like. As pure nickel, typically, NW2200, NW2201 prescribed in JIS G 4902:2019 can be used.

[0062] Note that the nickel-containing layer is not limited to the pure nickel layer as described above, and can be a Ni-based alloy layer in which Ni is the main component.

[0063] In order to suppress the formation of an Al-rich portion in the diffusion layer, it is more preferable that the content of Al in the nickel-containing layer is less. The content of Al in the nickel-containing layer is preferably 2.00% or less, more preferably 1.50% or less, and further preferably 1.00% or less. On the other hand, from the perspective of suppressing the increase in the cost of Al removal, or performing deoxidation of the material for the nickel-containing layer, and also adjusting the strength of the nickel-containing layer, the content of Al in the nickel-containing layer can be 0.005% or more, or can be 0.010% or more.

[0064] The thickness of the first layer and the third layer of the composite sheet of the present disclosure is preferably 30 μm or more and 300 μm or less, respectively. If the first layer and the third layer formed of pure nickel are made too thin, the bending processed portion of the layer constituting the outer side can be broken when subjected to severe bending processing. If the first layer or the third layer is broken, the second layer formed of carbon steel as a base material can be exposed, and the corrosion resistance in an alkaline environment can be significantly reduced. Therefore, the thickness of the first layer and the third layer is preferably 30 μm or more, respectively. From the perspective of suppressing exposure of the base material due to breakage of the mating material during bending processing, the thickness of the first layer and the third layer is more preferably 40 μm or more, and further preferably 50 μm or more, respectively.

[0065] On the other hand, if the first layer and the third layer are made too thick, the cost of the nickel billet can increase, and therefore the thickness of the first layer and the third layer is preferably 300 μm or less, respectively. From the perspective of cost, the thickness of the first layer and the third layer is more preferably 275 μm or less, respectively.

[0066] Note that the thickness of the first layer and the third layer can be the same, and it is also acceptable to set different thicknesses depending on the use.

[0067] (3) Second Layer (Iron-Based Alloy Layer)

[0068] The second layer is an iron-based alloy layer having Fe as the main component, and is preferably composed of carbon steel. As the carbon steel, SPCC, SPCD, SPCE, SPCF, and SPCG specified in JIS G 3141:2021 can be used, for example.

[0069] Note that the iron-based alloy constituting the second layer is not limited to carbon steel, and stainless steel, nickel-chromium steel, nickel-chromium-molybdenum steel, chromium steel, chromium-molybdenum steel, manganese steel, or the like can also be used.

[0070] In order to suppress the formation of Al-rich portions in the diffusion layer, it is more preferable that the Al content in the iron-based alloy layer be as low as possible. The Al content in the iron-based alloy layer is preferably 2.00% or less, more preferably 1.50% or less, and further preferably 1.00% or less. On the other hand, from the perspective of suppressing an increase in the cost of Al removal or performing deoxidation of the billet of the iron-based alloy layer, the Al content in the iron-based alloy layer can be 0.0005% or more, or 0.0010% or more.

[0071] (4) Diffusion Layer

[0072] The composite sheet of the present disclosure has a diffusion layer (not shown in the figure) in which Ni and Fe, which are the main constituent elements of the respective layers on the opposite sides, are mixed together by diffusion of each other, at a certain range of thickness, at the dissimilar metal interfaces between the first layer and the second layer and between the second layer and the third layer. Figure 1 ​

[0073] Figure 2 is a graph schematically showing the element composition distribution in the diffusion layer present in the vicinity of the dissimilar metal interface of the composite sheet of the present disclosure. In Figure 2 , for example, in the case where "Material A" is Ni and "Material B" is Fe, as shown in Figure 2 , when the element composition is measured in the thickness direction from the layer thickness center of the 1st layer or the 3rd layer, which are pure nickel layers, toward the 2nd layer, at each layer thickness center of the 1st layer and the 3rd layer, the composition of the pure nickel used as the raw material is respectively obtained, and when the measurement point approaches the vicinity of the dissimilar metal interface, the concentration of Fe, which is the main component of the 2nd layer, starts to gradually increase, and as the measurement point advances toward the 2nd layer, the concentration of Ni, which is the main component of the 1st layer and the 3rd layer, gradually decreases. The region where the Fe concentration gradually increases while the Ni concentration gradually decreases when scanning in the thickness direction is the diffusion layer. The diffusion layer is formed, for example, by stacking each raw material that constitutes the composite sheet, and in a state where the atoms of the interface of each raw material are bonded by metal bonds using rolling, pressure bonding, or the like, the atoms diffuse using thermal energy or the like, thereby forming a diffusion layer having an element concentration distribution as shown in Figure 2 .

[0074] The mechanical properties of the diffusion layer of the composite sheet of the present disclosure are different from the mechanical properties of the 1st layer and the 3rd layer and the mechanical properties of the 2nd layer. Furthermore, since it also has a concentration distribution, the mechanical properties of the diffusion layer are unstable. If the average thickness of the diffusion layer is greater than 10.0 μm, it is possible that the bonding strength of the dissimilar metal interface becomes unstable due to the diffusion layer, and it becomes easy for interface peeling to occur. Therefore, the average thickness of the diffusion layer is 10.0 μm or less. From the viewpoint of the stability of the mechanical properties of the dissimilar metal interface, it is preferable to be 9.5 μm or less, and more preferable to be 9.0 μm or less. On the other hand, if the diffusion layer is a certain range of average thickness, the dissimilar metal interface is moderately strengthened, which contributes to the improvement of the bonding strength. Therefore, the average thickness of the diffusion layer is 0.50 μm or more. From the viewpoint of the bonding strength, the average thickness of the diffusion layer is preferably 0.60 μm or more, and more preferably 0.70 μm or more.

[0075] Further, Al-rich portions having a granular shape are present in the diffusion layer, which are considered to originate from, for example, impurities in the nickel-containing metal forming the first layer and the third layer and / or the iron-based alloy forming the second layer. In the nickel-containing metal and the iron-based alloy manufactured industrially, Al from raw materials or as an element used in refining is inevitably contained. It is considered that Al-rich portions are likely to be formed in the diffusion layer from these Al components. The composite sheet of the present disclosure exhibits a concentration of Al of 15% or more by mass in the diffusion layer, and the number of granular Al-rich portions having an equivalent circle diameter of 250 nm or more is less than 0.50 per μm 2 .

[0076] The Al-rich portions in the vicinity of the dissimilar metal interface in a section perpendicular to the interface can be determined using a method of elemental analysis by an electron probe micro analyzer (EPMA), which are observed in a granular shape as described above. It is not necessarily clear what such Al-rich portions measured by EPMA actually correspond to, but if Al is enriched in the dissimilar metal interface based on the principle as described later, it is presumed to be an Al oxide, an oxide containing Al and Ni, Fe, and the like, or an intermetallic compound containing Al, and the like. The mechanical properties of these oxides, intermetallic compounds, and the like are different from those of the respective metals of the nickel-containing layer and the iron-based alloy layer contained in the region of the diffusion layer. Therefore, the mechanical properties of the diffusion layer in which a large number of coarse Al-rich portions are observed are unstable, and it is likely to be a major cause of interface peeling at the time of bending processing of the composite sheet and the like. The number of granular Al-rich portions having an equivalent circle diameter of 250 nm or more (coarse granular Al-rich portions) is less than 0.50 per μm 2 In the above case, interface peeling becomes likely to occur at the time of bending processing. Therefore, the number density of coarse granular Al-rich portions is less than 0.50 per μm 2 From the viewpoint of processability, it is preferable to be less than 0.40 per μm 2 .

[0077] The thickness of the diffusion layer and the Al-rich portions in the diffusion layer can be determined by elemental analysis based on EPMA along a plane (TD plane) normal to the rolling direction and the thickness direction of the composite sheet (Transverse direction; TD).

[0078] The thickness of the diffusion layer can be determined by EPMA line analysis of a cross section along the TD face of the plate. When line analysis is performed from the side of the first layer or the third layer, which is mainly composed of nickel, along a line parallel to the plate thickness direction on the TD face including the dissimilar metal interface, as described above, there is a region in which the Ni composition gradually decreases and the Fe composition gradually increases as the measurement point moves toward the second layer formed of an iron-based alloy. This region is a region affected by atomic interdiffusion at the interface, and the diffusion layer of the clad plate of the present disclosure is the region between the position at which the Fe composition shows 10% by mass and the position at which the Ni composition shows 10%. Therefore, by performing the EPMA line analysis as described above, the distance from the position at which the Fe composition shows 10% to the position at which the Ni composition shows 10% is measured at five or more different points at the dissimilar metal interface of the TD face of the plate at which the distance is 10 μm or more, and the average of these values is taken as the average thickness of the diffusion layer.

[0079] The determination of the Al-rich portion in the diffusion layer can be performed by the above-described EPMA surface analysis within the diffusion layer. Surface analysis is performed on a region including the diffusion layer, which is a cross section of the TD face, and within the diffusion layer of a prescribed area, all regions in which the Al concentration is 15% or more by mass are determined, and it is confirmed whether the area thereof is greater than the area of a circle having a diameter of 250 nm. The average thickness of the diffusion layer is 0.50 μm or more and 10.00 μm or less, and the investigation is performed at 20 μm 2 or more and 40 μm 2 or more within the diffusion layer, and if 0.50 or more Al-rich portions having an area greater than the area of a circle having a diameter of 250 nm are not observed per μm 2 or more, the diffusion layer can be considered to belong to the clad plate of the present disclosure. The EPMA device uses an EPMA equipped with a field emission (FE) type electron gun. As to the measurement conditions, the measurement is performed under conditions of an acceleration voltage of 15 kV, a beam diameter of 0.1 μm, and an irradiation time of 50 ms.

[0080] The main reason for the formation of the Al-rich portion within the diffusion layer having a certain range of average thickness as described above is not clear, and although it is only a conjecture, the following reasons can be considered.

[0081] It is considered that the formation of the Al-rich portion is affected by Al contained in the nickel-containing metal material and the Fe-based alloy material used in the production of the composite sheet of the present disclosure. As described above, for example, both pure nickel and carbon steel inevitably contain Al mixed from raw materials or Al used in a refining process. In a case where the materials serving as the materials of the composite sheet are heated separately in order to join the materials, an oxide film is formed by a reaction of the surface of the material with the atmosphere, but Al has a property of being oxidized even at a lower oxygen potential than Ni, which is the main element of the nickel-containing metal, and Fe, which is the main element of the Fe-based alloy.

[0082] For example, it is considered that, at the initial stage of oxidation, the most Ni and Fe present at the respective outermost surfaces of pure nickel and carbon steel are preferentially oxidized, and the oxidation progresses little by little from the outermost surface of each material toward the inside, and at a position where the oxygen potential decreases to a certain amount, an oxide containing Al is formed. Even if the atmosphere around the gap portion between the nickel-containing material and the Fe-based alloy material before the joining by rolling is sealed by welding or the like and the atmosphere is exhausted by a pump or the like, a complete vacuum is not formed. Therefore, it is difficult to completely suppress the formation of the oxide. Therefore, by the heating for joining, a state where a certain amount of Al oxide is formed on the surface of the material joint portion is caused. In the joining process of each material by rolling or the like, the Al-containing oxide is introduced into each layer in the vicinity of the heterogeneous metal interface by the effect of plastic flow at the interface or the like. It is considered that as a result, a portion in the vicinity of the heterogeneous metal interface within the nickel-containing layer or within the carbon steel layer, that is, a portion of the diffusion layer, is formed into the Al-rich portion enriched with Al in a granular form.

[0083] (5) Total thickness

[0084] The composite sheet of the present disclosure has a total thickness of more than 0.1 mm, regardless of a case where it is a two-layer structure of a first layer and a second layer or a case where it is a three-layer structure further including a third layer. In a case where the total thickness is more than 0.1 mm, it becomes easy to maintain a shape required as a material for a factory. From the viewpoint of shape maintenance, the total thickness of the composite sheet is preferably 0.2 mm or more, and more preferably 0.3 mm or more. On the other hand, in view of workability and cost when used as a material for a battery, a material for a salt electrolysis plant, and a material for an alkaline water electrolysis plant, the total thickness of the composite sheet is 3.0 mm or less. From the viewpoint of cost, the total thickness of the composite sheet is preferably 2.8 mm or less.

[0085] (6) Use

[0086] The composite sheet of the present disclosure exhibits high corrosion resistance in an environment immersed in an alkaline solution, and in addition, peeling at the interface between the nickel-containing layer mainly composed of Ni and the Fe-based alloy layer is not easily caused even when bending processing is performed.

[0087] The use of the composite sheet of the present disclosure is not particularly limited, and for example, can be suitably used for a material for a battery, a material for an alkaline water electrolysis plant, a cathode material for a salt electrolysis device used in the production of caustic soda as a basic industrial chemical, a gasket material, and the like. The composite sheet of the present disclosure is subjected to bending processing according to the use to produce a formed product having a desired shape.

[0088] The above description mainly describes a case where the diffusion layer at both interfaces in a 3-layer composite sheet satisfies the characteristics of the present disclosure (average thickness of the diffusion layer and number density of coarse granular Al-rich portions), but the composite sheet of the present disclosure can also be a 2-layer composite sheet, and the diffusion layer at only one of the two interfaces in a 3-layer composite sheet can satisfy the characteristics of the present disclosure.

[0089] In a case where bending processing of the composite sheet is performed, peeling is likely to occur in the nickel-containing layer on the outer peripheral surface side of the bending processed portion, and for example, in a case where the diffusion layer at the interface between only the first layer and the second layer in a 3-layer composite sheet satisfies the characteristics of the present disclosure, by performing bending processing in such a manner that the first layer side becomes the outer periphery (outer side) of the bending processed portion, occurrence of interface peeling can be suppressed.

[0090] [Method for manufacturing composite sheet]

[0091] Next, a preferred method for manufacturing the composite sheet of the present disclosure will be described. Note that the composite sheet of the present disclosure can obtain its effects as long as it has the above-described characteristics regardless of the manufacturing method. The method for manufacturing the composite sheet of the present disclosure is not limited, and can be stably manufactured according to the following method, and thus is preferred.

[0092] The composite sheet of the present disclosure can be manufactured through the following lamination process, roll bonding process, cold rolling process, and annealing process. Other processes can be included, and depending on the use, for example, a descaling process for removing scale formed on the surface of the sheet can be performed before the cold rolling process, or can be omitted.

[0093] Hereinafter, as an example of the method for manufacturing the composite sheet of the present disclosure, a method for manufacturing a 3-layer composite sheet in which a nickel-containing layer, an iron-based alloy layer, and a nickel-containing layer are sequentially laminated will be mainly described, but a 2-layer composite sheet in which a nickel-containing layer and an iron-based alloy layer are laminated can also be manufactured by the same method. Furthermore, regarding a part of the description, as a preferred form, a layer formed of pure nickel is described as the nickel-containing layer, and a layer formed of carbon steel is described as the iron-based alloy layer, but a blank of a Ni-based alloy or the like can be used as the nickel-containing layer, and a blank of stainless steel or the like can be used as the iron-based alloy layer.

[0094] [Lamination process]

[0095] The laminating step is a step of preparing a blank of the first layer, a blank of the second layer, and a blank of the third layer, laminating them in order, temporarily joining them at a portion of the outer peripheral portion by welding or the like, and producing a laminate.

[0096] [Roll joining step]

[0097] The roll joining step is a step of heating the laminate after the temporary joining to a certain temperature, directly performing hot joining rolling, and producing a joined body in which the first layer, the second layer, and the third layer are integrated.

[0098] [Cold rolling step]

[0099] The cold rolling step is a step of cold rolling the joined body to a prescribed thickness, and producing a clad plate.

[0100] [Annealing step]

[0101] The annealing step is a step of annealing the clad plate at a certain temperature in order to impart workability to the clad plate after the cold rolling.

[0102] Then, a preferred manufacturing method of the clad plate of the present disclosure includes the following steps as the above-described respective steps:

[0103] a laminating step of laminating, in a state in which a Fe-Ni alloy foil having a thickness of 0.050 mm or more and 0.125 mm or less, containing 35.0 to 65.0 mass% of Ni, 0.50 mass% or less of Al, and the balance being Fe and impurities, is arranged between a sheet of an iron-based alloy or an iron-based alloy blank as a thick plate and a sheet of a nickel-containing blank or a nickel-containing blank as a thick plate, welding a peripheral portion including a lengthwise end portion and a widthwise end portion, and producing a closed laminate;

[0104] a roll joining step of joining the iron-based alloy blank and the nickel-containing blank by hot rolling the laminate, and producing a joined body;

[0105] a cold rolling step of cold rolling the joined body, and producing a clad plate; and

[0106] an annealing step of annealing the clad plate (clad cold-rolled plate) after the cold rolling step at an annealing temperature T (°C) and an annealing time t (s) set to satisfy the following equation (1).

[0107] 0.010 ≤ 0.2958 × A × R × [0.001 × t × exp{-8596.1 / (T+273.15)}] 1 / 2 ≤ 0.200 (1)

[0108] In formula (1), A (mm) is the thickness of the Fe-Ni alloy foil inserted between the iron-based alloy blank and the nickel-containing blank in the lamination step, and R (%) is the rolling rate when the clad plate after the cold rolling step is made from the state of the laminate before the roll bonding step, and is calculated from the following formula (2).

[0109] R (%) = 100 x (X - W) / X (2)

[0110] In formula (2), X (mm) is the thickness of the laminate before the roll bonding step, and W (mm) is the plate thickness of the clad plate after the cold rolling step.

[0111] Hereinafter, each step will be described in order.

[0112] (1) Lamination step

[0113] In the lamination step, first, blanks for the 1st layer, the 2nd layer, and the 3rd layer are prepared, respectively. The shape is adjusted in a manner such that the thickness of each layer of the 1st layer, the 2nd layer, and the 3rd layer reaches the prescribed value described above when the completed clad plate is made. For example, as the blanks for the 1st layer and the 3rd layer, hot-rolled plates of pure nickel can be used, and as the blank for the 2nd layer, a plate blank of carbon steel can be used. These are laminated in the order of the 1st layer, the 2nd layer, and the 3rd layer in the thickness direction.

[0114] Before laminating the blanks, it is preferable to remove adherents such as scales from the positions corresponding to the bonding surfaces of each blank by polishing or the like. Furthermore, it is preferable to insert (arrange) foils of Fe-Ni alloy in the entire surface between the 1st layer and the 2nd layer, and between the 2nd layer and the 3rd layer in advance. By using the Fe-Ni alloy foil as the insertion material, a diffusion layer having a prescribed thickness with few Al-rich portions can be stably formed.

[0115] The Fe-Ni alloy foil used is mainly composed of Fe and Ni, and also contains impurities. Impurity elements can be exemplified by C, O, N, B, Si, P, S, Al, Ti, Nb, Mo, Mg, Ca, Mn, Cr, Co, Cu, and the like. The Ni composition (Ni content) of the Fe-Ni alloy foil is preferably 35.0 to 65.0% by mass. The Al concentration (Al content) in the Fe-Ni alloy foil is preferably 0.50% or less, and more preferably 0.30% or less.

[0116] Furthermore, the thickness of the Fe-Ni alloy foil is also related to the annealing step described later, and in order to stably exhibit the effect of the Fe-Ni alloy foil, it is preferably 0.050 mm or more. More preferably, it is 0.075 mm or more. On the other hand, if the thickness of the Fe-Ni alloy foil is too thick, there is a risk of an increase in alloy cost, and therefore the thickness is preferably 0.125 mm or less. More preferably, it is 0.110 mm or less.

[0117] After the laminated body obtained by laminating the material of the first layer, the material of the second layer, and the material of the third layer in this order by means of the Fe-Ni alloy foil between the material of the first layer and the material of the second layer and between the material of the second layer and the material of the third layer, in order to prevent the materials from moving, the outer peripheral portions between the materials of the first layer, the second layer, and the third layer of the laminated body are preferably temporarily fixed (welding packaging) by welding or the like. As the preferable welding method, electrode arc welding, TIG welding, MIG welding, and the like can be given. Further, at the time of welding or at a stage after welding, the space between the layers sealed by welding can be subjected to vacuum suction using a rotary pump or the like. The degree of vacuum is not particularly specified, but from the viewpoint of joint strength, it is preferably 5.0 x 10 -1 Pa or less.

[0118] (2) Rolling joint process

[0119] The rolling joint process is a process in which the laminated body obtained by the above-described method is subjected to hot rolling to joint the layers, thereby producing a joint body in which the layers are integrated. With respect to the heating temperature before hot rolling, in order to sufficiently obtain joint strength, heating to 900°C or higher is preferable. From the viewpoint of joint strength, 950°C or higher is more preferable. On the other hand, excessive increase in the heating temperature leads to an increase in the load on the heating equipment and an increase in energy costs, and thus the heating temperature is preferably 1350°C or lower. From the viewpoint of energy costs, 1300°C or lower is more preferable.

[0120] With respect to the pass schedule of rolling, if the reduction rate of the entire schedule is within a certain range, the rolling joint can be performed without problems. From the viewpoint of joint strength, the reduction rate is preferably 90.0% or higher throughout the schedule. On the other hand, excessive increase in the reduction rate leads to an increase in the load on the rolling equipment, and thus the reduction rate is preferably 98.5% or lower. From the viewpoint of the load on the rolling equipment, 98.4% or lower is more preferable. Note that the reduction rate can be calculated using the following formula (a).

[0121] Reduction rate (%) = 100 x (X - Y) / X (a)

[0122] Here, X (mm) is the thickness of the laminated body before the rolling joint, that is, the sum of the thicknesses of the material of the first layer, the material of the second layer, and the material of the third layer, and Y (mm) is the thickness of the joint body (sometimes referred to as a clad hot-rolled sheet or a hot-rolled sheet) after the rolling joint. Note that, since the thickness of the Fe-Ni alloy foil as an interposed material is sufficiently small compared to the thickness of each material before rolling, the thickness of the Fe-Ni alloy foil can be ignored when calculating X.

[0123] (3) Cold rolling process

[0124] For the composite hot-rolled plate joined by hot-rolling, after descaling as needed, in order to adjust the thickness to the prescribed value as a product, cold-rolling is performed. Descaling before cold-rolling can be omitted. In the pass schedule of rolling, if the rolling rate of the entire schedule is within a certain range, rolling can be performed without problems. The hot-rolled plate after the rolling joining process is thick for practically using as a material for a factory, so in order to perform thickness adjustment, it is preferable to perform cold-rolling of 30% or more at the minimum. On the other hand, if the rolling rate is excessively increased, it can lead to an increase in the load on the rolling equipment, so the rolling rate is preferably set to 95% or less. From the viewpoint of the load on the equipment, it is more preferable to be 94% or less.

[0125] (4) Annealing Process

[0126] In the cold-rolling process, the composite plate inevitably undergoes work hardening, and the workability decreases. Therefore, in order to obtain sufficient workability, annealing is performed. As for the annealing temperature, it is preferable to be performed at a temperature of 700°C or more at which both the layer of pure nickel and the layer of carbon steel undergo softening. From the viewpoint of promoting softening, it is more preferable to be 725°C or more. On the other hand, excessive temperature rise can lead to an increase in the load on the annealing equipment and an increase in energy costs, so the annealing temperature is preferably 1150°C or less. From the viewpoint of energy costs, it is more preferable to be 1100°C or less.

[0127] The annealing temperature and the annealing time in the annealing process are preferably within the range of the following formula (b).

[0128] 0.010≤B≤0.200 (b)

[0129] Note that the value of B in formula (b) is shown in the following formula (c).

[0130] B = 0.2958 x A x R x [0.001 x t x exp{-8596.1 / (T+273.15)}] 1 / 2 (c)

[0131] Here, A (mm) is the thickness of the Fe-Ni alloy foil inserted between each of the billets of the 1st layer and the 2nd layer and between each of the billets of the 2nd layer and the 3rd layer in the lamination process, R (%) is the rolling rate (also referred to as the total rolling rate) when the composite plate is made from the state of the laminate before rolling joining to after cold-rolling, t (s) is the annealing time, and T (°C) is the annealing temperature. R is found from the following formula (d).

[0132] R (%) = 100 x (X - W) / X (d)

[0133] Here, X (mm) is the thickness of the laminate before roll bonding, that is, the sum of the thicknesses of the blank of the first layer, the blank of the second layer, and the blank of the third layer, and W (mm) is the thickness of the clad plate after cold rolling. Note that the thickness of the Fe-Ni alloy foil as the interposed material is sufficiently thin compared to the sum X of the thicknesses of the respective blanks before rolling, and thus it is not problematic to ignore the thickness of the Fe-Ni alloy foil when calculating X.

[0134] In the above formula (b), if the annealing temperature and the annealing time are set so that the B value is less than 0.010, it becomes difficult to generate a stable diffusion layer of a certain thickness. Further, if the annealing temperature and the annealing time are set so that the B value is greater than 0.200, the diffusion layer tends to be thick, and it is likely that the mechanical properties of the dissimilar metal interface become easily unstable.

[0135] Regarding the effects of the interposition of the Fe-Ni alloy foil as described above and the control of the foil thickness of the interposed material, the rolling ratio from the state of the laminate before roll bonding, the annealing temperature, and the annealing time when the clad plate after cold rolling is produced, there are many unknowns, and although it is only a speculation, the following main reasons can be considered.

[0136] First, regarding the influence on the Al-rich portion in the diffusion layer, it is presumed that by suppressing the generation amount of oxides per unit area of the respective blanks of the first layer and the second layer and the respective blanks of the second layer and the third layer, there is an effect of suppressing the formation of the Al-rich portion. Although there are many unknowns regarding the generation behavior of the oxides containing Al on the surfaces of the respective layers of the blanks and the Fe-Ni alloy foil, at least by disposing the metal foil in the gap portion between the blanks, the area where the metal reacts with the atmosphere increases, and the reaction amount of oxygen per unit area of the metal, that is, the degree of oxidation becomes small. By suppressing the degree of oxidation per unit area of the metal surface, only the surface of each metal blank is oxidized, and the oxidation reaction becomes difficult to proceed to the inside. In the case where only the surface is oxidized in a small amount, as in the initial stage of oxidation in the conventional atmosphere, not an element that is likely to bind with oxygen is oxidized, but oxidation preferentially occurs from the elements present on the surface. That is, it is considered that oxidation of Ni and Fe on the surface of each blank of pure nickel and carbon steel preferentially occurs, and Al becomes less likely to be oxidized.

[0137] Further, regarding the influence on the thickness of the diffusion layer, it is presumed that by using the interposed material and appropriately performing heat treatment, the thickness can be controlled within a prescribed range. It is considered that in the case where the interposed material is not used, the diffusion layer is formed in the hot roll bonding process or the annealing process after the pure nickel and the carbon steel are tightly bonded and joined in the roll bonding process, but the interface where the pure nickel and the carbon steel are joined by rolling is not necessarily flat, and the application of the press is not uniform, and thus the formation of the diffusion layer thereafter becomes difficult to be uniform and becomes unstable.

[0138] On the other hand, it can be considered that by using the Fe-Ni alloy foil as the interposed material, by uniformly forming a layer in which Fe and Ni are mixed in advance, it becomes easy to form a stable diffusion layer of uniform thickness after joining. On this basis, it is also necessary to appropriately adjust the annealing conditions, particularly the annealing temperature and time, in the annealing process in which the state of the diffusion layer inevitably changes, and thereby appropriately manage the thickness distribution of the diffusion layer. The aforementioned content described in formula (b) is an empirical formula, in which there is a portion considered to correspond to the thickness assumed after cold rolling of the Fe-Ni alloy foil interposed in the lamination process, and a portion considered to correspond to the diffusion distance in the annealing process. That is, it is presumed that it is composed of parameters that affect the formation and growth of the diffusion layer in the manufacturing process of the clad plate. It is presumed that therefore by controlling this formula (b) within a certain range empirically obtained, the thickness of the diffusion layer is stably formed within the prescribed range of the clad plate of the present disclosure.

[0139] The manufacturing method of the clad plate of the present disclosure is not limited to the above-described method, and the clad plate of the present disclosure can be manufactured without using the Fe-Ni alloy foil.

[0140] Examples

[0141] Hereinafter, the effects of the present disclosure will be described by examples, but the present disclosure is not limited to the conditions used in the following examples.

[0142] As the raw material of the 1st layer and the 3rd layer of the clad plate, pure nickel NW2201 or nickel-based alloy NCF600 was used, and as the raw material of the 2nd layer, carbon steel SPCC, SPCE, or stainless steel SUS304 was used.

[0143] Using these respective raw materials, a 3-layer clad plate in which the 1st layer, the 2nd layer, and the 3rd layer were sequentially stacked, or a 2-layer clad plate in which the 1st layer and the 2nd layer were sequentially stacked, was manufactured through the above-described lamination process, the roll joining process, the scale removal process, the cold rolling process, and the annealing process. The scale removal process was omitted for a part.

[0144] Further, for a part of the clad plates, a foil of an Fe-Ni alloy containing 50% of Ni and the balance of Fe and impurities in terms of mass% was disposed between the respective raw materials of the 1st layer and the 2nd layer, and between the respective raw materials of the 2nd layer and the 3rd layer in the lamination process. In addition, for a part of the clad plates, a foil of the Fe-Ni alloy was disposed between the respective raw materials of the 1st layer and the 2nd layer, and on the other hand, was not disposed between the respective raw materials of the 2nd layer and the 3rd layer. Note that, regarding the thickness of the raw material, the raw material was adjusted to the thickness described later using the rolling rate of the roll joining process and the cold rolling process.

[0145] In the production of each composite sheet, the thickness A (mm) of the Fe-Ni alloy foil interposed material, the rolling ratio R (%) of the total thickness from the lamination step to the cold rolling step, the temperature T (°C) in the annealing step, and the time t (s) were changed. Based on these values, the B value of formula (c) was calculated. In addition, the descaling step was performed by surface grinding.

[0146] For each of the produced composite sheets, with respect to the region in the vicinity of the dissimilar metal interface of the plate cross section along the TD plane, the 3-layer composite sheet was with respect to the interface of the 1st layer and the 2nd layer and the interface of the 2nd layer and the 3rd layer, and the 2-layer composite sheet was with respect to the interface of the 1st layer and the 2nd layer, EPMA line analysis in the plate thickness direction was performed at 5 places each, and the average thickness of the diffusion layer was measured.

[0147] In addition, EPMA surface analysis was performed on an area of 30 μm 2 of each diffusion layer, and the number density of the granular Al-rich portion with an equivalent circle diameter of 250 nm or more (denoted as “coarse Al-rich portion” in Table 2) was investigated. Note that, for the 3-layer composite sheet, in the case where the number density of the coarse Al-rich portion in the diffusion layer of the two interfaces was different, the evaluation is described in Table 2 for each interface.

[0148] [Assessment]

[0149] [Bending Test]

[0150] As the bending test, the press bending method according to JIS Z2248:2022 was performed. The width of the bending test piece was 10 mm, the inside radius was 4 mm, the radius of the support body was 14 mm, and the bending angle was 45° and 90°. Note that, the bending test was performed in such a manner that the outer periphery (outside) of the bending processed portion was constituted by the 1st layer side.

[0151] In the 45° bending test, the case where peeling occurred locally or entirely at the dissimilar metal interface was denoted as “Yes”, and the case where peeling did not occur was denoted as “No”. In addition, after the 90° bending test, the case where the 1st layer was broken and the 2nd layer was exposed was denoted as “Yes”, and the case where the 2nd layer was not exposed was denoted as “No”. Note that, in the 90° bending test, even in the case where wrinkles and cracks were generated in the 1st layer, the case where the 2nd layer was not exposed was denoted as “No”. The breaking of the 1st layer is not directly related to the problem of the present disclosure, but the test material for which the determination was “No” has a higher degree of freedom in bending processing, and thus is preferred.

[0152] The blank, the number of layers, and the manufacturing conditions of each composite sheet are shown in Table 1, and the thickness, the results of the EPMA analysis, and the bending test results of each composite sheet are shown in Table 2.

[0153]

[0154]

[0155] Nos. 1 to 9 and 12 to 14 are composite sheets of the present disclosure.

[0156] As is clear from Table 2, Nos. 1 to 9, 13, and 14 are confirmed to be less likely to cause peeling at the dissimilar metal interface even in the bending test (45° bending), and in addition, less likely to cause breakage of the first layer (90° bending), and are particularly suitable for use as a blank for a use requiring a large bending process.

[0157] Note that No. 8 has a thickness of the diffusion layer and a number density of coarse Al-rich portions at the interface between the first layer and the second layer on the outside of the bending process portion where peeling or breakage is likely to occur, within the range of the present disclosure, and does not cause peeling or breakage in either of the 45° bending and the 90° bending.

[0158] No. 12 did not cause interface peeling in the 45° bending test, but the thicknesses of the first layer and the third layer were thin, and the first layer broke and the second layer was exposed in the 90° bending test.

[0159] No. 14 has a high number density of coarse Al-rich portions in the diffusion layer, although within the permissible range, because of the high Al concentration in the Fe-Ni alloy foil. Therefore, although it did not cause interface peeling in the 45° bending test, it caused peeling at the interface in the 90° bending test.

[0160] Nos. 10 and 11 did not sufficiently anneal after the roll bonding process, and the thickness of the diffusion layer was too thin, and caused peeling at the interface in the 45° bending test.

[0161] No. 15 caused peeling at the interface in either of the 45° bending test and the 90° bending test because of the high number density of coarse Al-rich portions in the diffusion layer, which exceeds the upper limit of the present disclosure, due to the high Al concentration in the Fe-Ni alloy foil used.

[0162] The disclosure of Japanese Patent Application No. 2023-072770 filed on April 26, 2023 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards identified in this specification are incorporated by reference herein to the same extent as if each individual document, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

[0163] Explanation of symbols

[0164] 1 Composite sheet

[0165] 2 First layer (nickel-containing layer)

[0166] 3 Second layer (iron-based alloy layer)

[0167] 4 3rd layer (Ni-containing layer)

Claims

1. A composite plate comprising an iron-based alloy layer formed of an iron-based alloy, and a nickel-containing layer laminated on one or both sides of the iron-based alloy layer and having Ni as the main component. The total thickness of the composite panel is greater than 0.1 mm and less than 3.0 mm. Between at least one side of the iron-based alloy layer and the nickel-containing layer, a diffusion layer with Ni and Fe concentrations of 10% by mass or more exists with an average thickness of 0.50 μm or more and 10.0 μm or less. Within the diffusion layer, in a cross-section containing the diffusion layer and with a normal to a direction perpendicular to the rolling direction and the plate thickness direction, the number density of granular Al-rich portions with an Al concentration of 15% by mass or more and an equivalent circle diameter of 250 nm or more is less than 0.50 particles / μm. 2 .

2. The composite board according to claim 1, wherein, The nickel-containing layer is stacked on both sides of the iron-based alloy layer, and the diffusion layer exists between the iron-based alloy layer and the nickel-containing layer. In each of the diffusion layers in the cross-section, the number density of the granular Al-enriched portions is less than 0.50 particles / μm. 2 .

3. The composite board according to claim 1, wherein, The thickness of the nickel-containing layer is more than 30 μm and less than 300 μm.

4. A method for manufacturing a composite panel, comprising the steps described in any one of claims 1 to 3: The lamination process involves stacking Fe-Ni alloy foil between one or both sides of an iron-based alloy slab or a thick iron-based alloy slab and a nickel-containing slab or a thick nickel-containing slab, wherein the Fe-Ni alloy foil has a thickness of 0.050 mm or more and 0.125 mm or less, contains 35.0 to 65.0% by mass of Ni, 0.50% by mass of Al or less, and the balance is Fe and impurities. The periphery, including the ends in the length direction and the ends in the width direction, is welded and sealed to form a sealed laminate. The rolling joining process involves hot rolling the laminate to join the iron-based alloy billet and the nickel-containing billet to form a joined body. A cold rolling process is performed to cold roll the joint to produce a composite plate; and In the annealing process, for the composite plate after the cold rolling process, the annealing temperature T (°C) and annealing time t (s) are set to satisfy the following equation (1): 0.010≤0.2958×A×R×[0.001×t×exp{-8596.1 / (T+273.15)}] 1 / 2 ≤0.200 (1), In equation (1), A (mm) is the thickness of the Fe-Ni alloy foil, and R (%) is the rolling rate when the composite plate after the cold rolling process is made from the state of the laminate before the rolling joining process, which is obtained by the following equation (2): R(%)=100×(XW) / X (2), In the formula (2), X (mm) is the thickness of the laminate before the rolling bonding process, and W (mm) is the thickness of the composite plate after the cold rolling process.

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