Clad plate and method for manufacturing the same

Abstract

A clad sheet 1 comprises: an iron-based alloy layer 3 made of an iron-based alloy; and a nickel-containing layer 2, 4 formed on one or both surfaces of the iron-based alloy layer and comprising Ni as a main component. The total thickness is larger than 0.1 mm but not larger than 3.0 mm. Between at least one surface of the iron-based alloy layer and the nickel-containing layer, a diffusion layer having an Ni concentration of 10 mass% or higher and an Fe concentration of 10 mass% or higher is present in an average thickness of 0.50-10.0 μm. In a cross-section which includes the diffusion layer and for which the direction perpendicular to both the rolling direction and the sheet thickness direction is normal, the number density of Al-enriched grains in the diffusion layer is less than 0.50 grains / μm2, the Al-enriched grains having an Al concentration of 15 mass% or higher and an equivalent circle diameter of 250 nm or larger.

Description

[Technical Field]

[0001] This disclosure relates to clad plates and methods for manufacturing the same. [Background technology]

[0002] Nickel exhibits high corrosion resistance in environments where it is immersed in alkaline solutions. For this reason, it is often used in applications where alkali corrosion resistance is required, such as in the cathode material and baking material of salt electrolytic equipment used in the production of caustic soda, a basic industrial chemical. In recent years, technologies that realize a carbon-neutral society have attracted attention in order to mitigate climate change caused by greenhouse gases such as carbon dioxide. In particular, nickel materials for the utilization of hydrogen energy, such as nickel used as electrode materials for secondary batteries used in various electrification technologies such as electric vehicles, electrodes for alkaline water electrolysis devices, and baking materials, are expected to see increased demand in the future. Nickel materials used in these applications are sheets made from a single pure nickel metal.

[0003] On the other hand, nickel metal is expensive, and its price tends to fluctuate sharply due to changes in the global supply and demand balance of nickel ore. In the future, demand for nickel is expected to surge in order to realize the aforementioned carbon-neutral society.

[0004] As mentioned earlier, nickel has extremely high corrosion resistance in alkaline environments. Therefore, thinning of nickel during use in alkaline environments is unlikely to be a problem. For this reason, it may be possible to reduce material costs by using a sheet material in which the inner layer is made of a general-purpose and inexpensive metal material and the outer layer is made of nickel.

[0005] One method for manufacturing such a multi-layered sheet material is to apply nickel plating to the surface of a general-purpose metal, such as carbon steel. Patent Document 1 discloses a highly corrosion-resistant nickel-plated steel strip in which a nickel plating layer is formed on one or both sides of a carbon steel sheet, and part or all of the nickel plating layer forms a nickel-iron diffusion layer, with the exposure rate of iron at the outermost surface of the nickel plating layer being 30% or less. Such nickel plating can be achieved by forming the nickel plating layer by electrolytic plating or electroless plating using a catalyst, and by applying post-plating heat treatment as necessary. While multilayer materials created by plating can reduce the amount of nickel used, there is a risk of iron exposure occurring in bent sections when used in plants and other industrial settings. Therefore, there is a growing demand for multilayer materials with a nickel layer thickness greater than that achievable by plating alone.

[0006] As an example of multi-layered steel sheets other than plating, there are clad materials, which involve joining a cladding material that imparts new functionality to the surface of a base material made of a general-purpose metal. For example, Patent Document 2 discloses a method for obtaining a clad sheet by hot-rolling an assembled material, which is made by overlapping a carbon steel base material with a cladding material made of one of the following: stainless steel, pure nickel, or a nickel alloy, and welding the edges together. In the example of Patent Document 2, a clad steel sheet with a rolled finish thickness of 30 mm is produced.

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 6-2104 Patent document 2: Japanese Patent Application Laid-open No. 192404 / 1999 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The nickel-clad plates disclosed in Patent Document 2 and those specified in JIS G 3602:2012 are thick, and in particular, the JIS specification only specifies that the thickness of the outer nickel layer of the cladding material should be 1 mm or more, less than 5 mm, or 5 mm or more.

[0009] Currently, there is high demand for nickel metal components used in electrolytic devices in alkaline environments. From the viewpoint of reducing material costs, plates with a thickness of 3 mm or less are preferred. Therefore, it is preferable to keep the thickness of the nickel-containing layer of the nickel-clad plate used as a substitute, as well as the thickness of the clad plate itself, to the absolute minimum necessary.

[0010] As disclosed in Patent Document 2, Fe-Ni cladding in the form of thick plates has already been put into practical use. On the other hand, Fe-Ni cladding in the form of thin plates with a thickness of 3 mm or less has not been known until now. In the case of thin plates, while it is possible to manufacture thin plates with a precise adjustment of the total thickness using manufacturing processes such as cold rolling, which are difficult to apply to thick plates, generally a greater bending angle is required than for thick plates.

[0011] For example, when using a clad sheet, which is made by laminating carbon steel as the base material and nickel as the cladding material, and joining them by interdiffusion, as a substitute for a conventional nickel-only sheet, problems arise such as delamination at the layer interface in the bent section and exposure of the base material due to fracture of the cladding material. Unlike single-material clad sheets, clad sheets have an interface between nickel and carbon steel (hereinafter referred to as the dissimilar metal interface) inside the sheet. Nickel and carbon steel have different mechanical properties and deformation behaviors, and furthermore, the dissimilar metal interface itself has different mechanical properties. For these reasons, it is desirable to develop a clad sheet in which a nickel-based cladding material is mainly composed of an iron-based alloy such as carbon steel as the base material, which is less prone to interfacial delamination at the dissimilar metal interface in bending processes beyond a certain size, and preferably a material that is even less prone to exposure of the core material due to fracture of the cladding material.

[0012] This disclosure has been made in view of the above-mentioned problems. Specifically, the object of this disclosure is to provide a clad sheet that is less prone to interfacial delamination between the nickel-containing layer, which is mainly composed of Ni, and the iron-based alloy layer, even when subjected to bending. [Means for solving the problem]

[0013] The above problems will be solved by the following means. [1] comprising an iron-based alloy layer made of an iron-based alloy, and a nickel-containing layer mainly composed of Ni, laminated on one or both sides of the iron-based alloy layer, The total thickness is greater than 0.1 mm and less than or equal to 3.0 mm. Between at least one side of the iron-based alloy layer and the nickel-containing layer, there exists a diffusion layer with an average thickness of 0.50 μm to 10.0 μm, in which the concentrations of Ni and Fe are both 10% by mass or more, and within the diffusion layer, including the diffusion layer, in a cross-section normalized to the direction perpendicular to the rolling direction and the thickness direction, the Al concentration is 15% by mass or more, and the number density of granular Al-enriched portions with an equivalent circle diameter of 250 nm or more is 0.50 pieces / μm 2 A clad plate that is less than [a certain value]. [2] The nickel-containing layer is laminated on both sides of the iron-based alloy layer, and the diffusion layer is present between both sides of the iron-based alloy layer and the nickel-containing layer, and the number density of the granular Al-enriched portion is 0.50 particles / μm² within each of the diffusion layers in the cross-section. 2 A cladding plate as described in [1], which is less than [1]. [3] The clad plate according to [1] or [2], wherein the thickness of the nickel-containing layer is 30 μm or more and 300 μm or less. [4] A lamination process 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% Ni and 0.50 mass% or less Al, with the remainder being Fe and impurities, is laid between one or both sides of an iron-based alloy material, which is an iron-based alloy slab or plate, and a nickel-containing material, which is a nickel-based alloy slab or plate, and the surrounding area, including the longitudinal and widthwise ends, is welded to seal the laminate, A rolling joining step of joining the iron-based alloy material and the nickel-containing material by hot-rolling the laminate to form a joined body; A cold rolling step of cold-rolling the joined body to form a clad plate; An annealing step of annealing the clad plate after the cold rolling step by setting the annealing temperature T (°C) and the annealing time t (s) to satisfy the following formula (1); A method for manufacturing a clad plate, including the steps of manufacturing the clad plate according to any one of [1] to [3]. 0.010 ≤ 0.2958×A×R×[0.001×t×exp{-8596.1 / (T + 273.15)}] 1 / 2 ≤ 0.200 ··· (1) In the formula (1), A (mm) is the thickness of the Fe-Ni alloy foil, and R (%) is the rolling rate when the laminate before the rolling joining step is made into the clad plate after the cold rolling step, which is obtained from the following formula (2). R (%) = 100×(X - W) / X ··· (2) In the formula (2), X (mm) is the thickness of the laminate before the rolling joining step, and W (mm) is the plate thickness of the clad plate after the cold rolling step.

Advantages of the Invention

[0014] According to the present disclosure, a clad plate is provided in which interfacial delamination between a nickel-containing layer mainly composed of Ni and an iron-based alloy layer is unlikely to occur even when bending is performed.

Brief Description of the Drawings

[0015] [Figure 1] An explanatory diagram showing the overall configuration of an example of the clad plate according to the present disclosure. [Figure 2] A diagram schematically showing the elemental composition distribution in the diffusion layer existing near the dissimilar metal interface of the clad plate according to the present disclosure.

Embodiments for Carrying Out the Invention

[0016] An example of an embodiment of this disclosure will be described. In this disclosure, a numerical range represented by "~" means a range that includes the numbers before and after "~" as the lower and upper limits. However, if the numbers before and after "~" are preceded by "greater than" or "less than", the numerical range means a range that does not include those numbers as the lower or upper limit. In chemical composition, the percentage "%" indicates "mass percent". When the chemical composition of an element is described as "0~", it means that the element does not need to be included. The term "process" includes not only independent processes, but also any process that cannot be clearly distinguished from other processes, as long as its intended purpose is achieved.

[0017] The inventors of this disclosure have diligently studied the above-mentioned problems and have obtained the following findings.

[0018] (A) In nickel and carbon steel clad sheets joined by hot rolling, a layer of diffused elements (hereinafter referred to as the diffusion layer) exists near the interface between the dissimilar metals. The diffusion layer is inevitably formed when the materials of each layer are laminated and joined by hot rolling or pressing. The diffusion layer does not disappear even when the hot-joined sheet is processed into a thin sheet by cold working such as cold rolling.

[0019] (B) When the thickness of the diffusion layer is below a certain level, tiny voids may form at the interface between dissimilar metals when bending is performed. Similarly, even if the thickness of the diffusion layer exceeds a certain level due to heat treatment or other processes, voids may still form at the interface when bending is performed.

[0020] (C) Furthermore, the diffusion layer may contain regions where granular Al is concentrated (hereinafter referred to as Al-enriched regions), which are thought to originate from nickel as a refining element or impurity, and Al which is inevitably contained in carbon steel.

[0021] (D) If a certain amount or more of Al-enriched areas with a diameter of a certain size or larger are present in the diffusion layer, when bending is performed, there is a possibility that minute voids may form between the nickel-containing layer and the carbon steel layer, or that delamination may occur.

[0022] (E) If a nickel / carbon steel interface can be formed in which the diffusion layer thickness is within a certain range and granular Al-enriched areas with a certain diameter or larger are absent or present only in small amounts, then interfacial delamination during bending is less likely to occur.

[0023] (F) If the thickness of the nickel-containing layer, which is the cladding material, is below a certain level, when bending the cladding plate, if the nickel-containing layer is present on the outer periphery of the bend (the surface that is outside the bent part), the nickel-containing layer may rupture, and the carbon steel base material may be exposed.

[0024] The clad plate relating to this disclosure was created based on the above-mentioned findings.

[0025] [Clad plate] (1) Overall structure The clad sheet according to this disclosure comprises an iron-based alloy layer made of an iron-based alloy, and a nickel-containing layer mainly composed of Ni, laminated on one or both sides of the iron-based alloy layer. The clad sheet according to this disclosure has a total thickness of more than 0.1 mm and 3.0 mm or less. Between at least one side of the iron-based alloy layer and the nickel-containing layer, there exists a diffusion layer with an average thickness of 0.50 μm or more and 10.0 μm or less, in which the concentrations of Ni and Fe are both 10 mass% or more. Furthermore, within the diffusion layer, including the diffusion layer, in a cross-section normalized to the direction perpendicular to the rolling direction and the thickness direction, the number density of granular Al-enriched parts is 0.50 particles / μm, in which the Al concentration is 15 mass% or more and the equivalent circle diameter is 250 nm or more. 2 It is less than.

[0026] The clad plate according to this disclosure may be a two-layer clad plate in which one iron-based alloy layer and one nickel-containing layer are laminated, or a three-layer clad plate in which an iron-based alloy layer is laminated between two nickel-containing layers. In the case of a three-layer clad plate, diffusion layers exist at the two interfaces between the nickel-containing layer and the iron-based alloy layer, and either one of the diffusion layers satisfies the above conditions, or both diffusion layers satisfy the above conditions. From the viewpoint of suppressing interfacial delamination regardless of the bending direction of the clad plate, it is preferable that both diffusion layers satisfy the above conditions. Hereinafter, as an example of a clad plate relating to this disclosure, a three-layer clad plate in which a nickel-containing layer, an iron-based alloy layer, and another nickel-containing layer are laminated in that order will be mainly described with reference to the drawings. In the following description, reference numerals in the figures will be omitted as appropriate. Furthermore, in a preferred embodiment, the nickel-containing layer may be described as a layer made of pure nickel, and the iron-based alloy layer as a layer made of carbon steel.

[0027] Figure 1 is an explanatory diagram showing the overall structure of an example of cladding according to this disclosure. As shown in Figure 1, the cladding plate 1 comprises a first layer 2, a second layer 3, and a third layer 4. The second layer 3 is an iron-based alloy layer mainly composed of Fe, and the first layer 2 and the third layer 4 are nickel-containing layers mainly composed of Ni. In this disclosure, the "main component" of a layer means the element that has the highest content (mass%) among the elements constituting that layer.

[0028] The second layer 3 is joined to the first layer 2 via one of its two surfaces (front and back). The second layer 3 is joined to the third layer 4 via the other of its two surfaces (front and back). At the interface between the first layer 2 and the second layer 3 of the clad plate of this disclosure, and at the interface between the second layer 3 and the third layer 4, there is a diffusion layer of a certain thickness in which Ni and Fe, the main constituent elements of each layer, are mixed by diffusion. Within this diffusion layer, Al-enriched areas may be formed, which are thought to be formed by nickel and Al, which is an element used in the refining of carbon steel or is mixed in as an impurity. However, in the clad plate of this disclosure, within the diffusion layer, there is a circular equivalent diameter of 250 nm or less. The Al-enriched area shown above is either absent or present only in small amounts.

[0029] (2) The first and third layers (nickel-containing layers) The first and third layers are nickel-containing layers with Ni as the main component (for example, 50% or more), and are preferably composed of pure nickel. The pure nickel suitable for use as a material for manufacturing the clad plates of this disclosure preferably contains 98% or more Ni by mass, and more preferably 99% or more Ni, in its elemental composition. The remainder consists mainly of impurities introduced from the raw materials or used in the refining process. Examples of impurity elements include C, O, N, B, Si, P, S, Al, Ti, Nb, Mo, Mg, Ca, Mn, Cr, Co, Cu, Fe, etc. As pure nickel, NW2200 and NW2201 as specified in JIS G 4902:2019 can be used as representative examples. Furthermore, the nickel-containing layer is not limited to a pure nickel layer as described above, but may also be a nickel-based alloy layer with Ni as the main component. To suppress the formation of Al-enriched areas in the diffusion layer, a lower Al content in the nickel-containing layer is preferable. The Al content in the nickel-containing layer is preferably 2.00% or less, more preferably 1.50% or less, and even more preferably 1.00% or less. On the other hand, from the viewpoint of suppressing the increase in Al removal costs, deoxidizing the material of the nickel-containing layer, or adjusting the strength of the nickel-containing layer, the Al content in the nickel-containing layer may be 0.005% or more, or 0.010% or more.

[0030] The thicknesses of the first and third layers of the clad plate according to this disclosure are preferably 30 μm or more and 300 μm or less, respectively. If the first and third layers, which are made of pure nickel, are made too thin, the bent portion of the outer layer may break when subjected to severe bending. If the first or third layer breaks, the base material, the second layer made of carbon steel, will be exposed, and the corrosion resistance of that area in an alkaline environment will be significantly reduced. For this reason, the thicknesses of the first and third layers are preferably 30 μm or more. From the viewpoint of suppressing the exposure of the base material due to the breakage of the cladding material during bending, the thicknesses of the first and third layers are more preferably 40 μm or more, and even more preferably 50 μm or more. On the other hand, if the first and third layers are made excessively thick, the cost of nickel material will increase, so it is preferable that the thickness of the first and third layers be 300 μm or less. From a cost standpoint, it is even more preferable that the thickness of the first and third layers be 275 μm or less. The thicknesses of the first and third layers can be the same, or they can be different depending on the application.

[0031] (3) Second layer (iron-based alloy layer) The second layer is an iron-based alloy layer with Fe as the main component, and is preferably made of carbon steel. Typical carbon steels that can be used are SPCC, SPCD, SPCE, SPCF, and SPCG as specified in JIS G 3141:2021. Furthermore, the iron-based alloy constituting the second layer is not limited to carbon steel; for example, stainless steel, nickel-chromium steel, nickel-chromium-molybdenum steel, chromium steel, chromium-molybdenum steel, and manganese steel can also be used. To suppress the formation of Al-enriched areas in the diffusion layer, a lower Al content in the iron-based alloy layer is preferable. The Al content in the iron-based alloy layer is preferably 2.00% or less, more preferably 1.50% or less, and even more preferably 1.00% or less. On the other hand, from the viewpoint of suppressing the increase in Al removal costs or deoxidizing the material of the iron-based alloy layer, the Al content in the iron-based alloy layer may be 0.0005% or more, or 0.0010% or more.

[0032] (4) Diffusion layer In the clad plate according to this disclosure, a diffusion layer (not shown in Figure 1) exists with a certain thickness at the dissimilar metal interface between the first layer and the second layer, and between the second layer and the third layer, in which Ni and Fe, the main constituent elements of the opposing layers, are mixed by their respective diffusion. Figure 2 schematically shows the elemental composition distribution in the diffusion layer near the dissimilar metal interface of the clad plate according to this disclosure. In Figure 2, for example, if "Material A" is Ni and "Material B" is Fe, as shown in Figure 2, when the elemental composition is measured along the thickness direction of the plate, from the center of the thickness of the first or third layer, which is a pure nickel layer, toward the second layer, the composition at the center of the thickness of the first and third layers is that of the pure nickel used as the material, but as the measurement point approaches the vicinity of the dissimilar metal interface, the concentration of Fe, the main component of the second layer, begins to gradually increase, and as the measurement point moves toward the second layer, the concentration of Ni, the main component of the first and third layers, gradually decreases. The region in which the Fe concentration gradually increases and the Ni concentration gradually decreases when scanning in the thickness direction is the diffusion layer. The diffusion layer is, for example, each material constituting the clad plate. By stacking these materials and then rolling or pressing them together, the atoms at the interface of each material are joined by metallic bonds. As the atoms diffuse due to thermal energy, a diffusion layer with an elemental concentration distribution as shown in Figure 2 is formed.

[0033] The mechanical properties of the diffusion layer of the clad plate according to this disclosure differ from those of the first and third layers and the second layer. Furthermore, due to the concentration distribution, the mechanical properties of the diffusion layer are unstable. If the average thickness of the diffusion layer exceeds 10.0 μm, the bonding strength of the dissimilar metal interface becomes unstable due to the diffusion layer, and interfacial delamination may occur more easily. 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 preferably 9.5 μm or less, more preferably 9.0 μm or less. On the other hand, if the diffusion layer has an average thickness within a certain range, the dissimilar metal interface is moderately strengthened, contributing to improved bonding strength. Therefore, the average thickness of the diffusion layer is 0.50 μm or more. From the viewpoint of bonding strength, the average thickness of the diffusion layer is preferably 0.60 μm or more, more preferably 0.70 μm or more.

[0034] Furthermore, the diffusion layer contains granular Al-enriched regions, which are thought to originate from impurities in the nickel-containing metals forming the first and third layers and / or the iron-based alloy forming the second layer. Industrially manufactured nickel-containing metals and iron-based alloys inevitably contain Al, either from the raw materials or as an element used in refining. It is thought that these Al components are likely the origin of the Al-enriched regions that form within the diffusion layer. In the clad plate according to this disclosure, granular Al-enriched regions with a mass% Al concentration of 15% or more and an equivalent circle diameter of 250 nm or more are present in the diffusion layer at a concentration of 0.50 particles / μm in a cross section normalized to the direction perpendicular to the rolling direction and the plate thickness direction, including the diffusion layer. 2 It is less than.

[0035] Al-enriched areas can be identified in the vicinity of the dissimilar metal interface, in a cross-section perpendicular to the interface, using elemental analysis with an electron probe microanalyzer (EPMA), and as mentioned above, they are observed in a granular form. It is not entirely clear what these Al-enriched areas measurable by EPMA actually correspond to, but if Al is enriched at the dissimilar metal interface by the principle described later, it is presumed to be Al oxide, an oxide containing multiple metals such as Al, Ni, and Fe, or an intermetallic compound containing Al. These oxides and intermetallic compounds all have different mechanical properties from the nickel-containing layer and the iron-based alloy layer contained in the diffusion layer region. Therefore, a diffusion layer in which many coarse Al-enriched areas are observed has unstable mechanical properties and may become a cause of interfacial delamination during bending of the clad plate. Granular Al-enriched regions (coarse-grained Al-enriched regions) with an equivalent circular diameter of 250 nm or more are present in the diffusion layer within a cross-section normalized to the direction perpendicular to the rolling direction and the thickness direction, including the diffusion layer, at a rate of 0.50 particles / μm. 2 If the above conditions are present, interfacial delamination is more likely to occur during bending. Therefore, the number density of coarse-grained Al-enriched areas should be 0.50 particles / μm 2 The particle size is less than 0.40 particles / μm, and from the viewpoint of processability, it is preferably 0.40 particles / μm. 2 It is less than.

[0036] The thickness of the diffusion layer and the Al-enriched areas within the diffusion layer can be measured by elemental analysis using EPMA along a plane (TD plane) whose normality is perpendicular to the direction perpendicular to the rolling direction and thickness direction of the cladding plate (Transverse direction; TD). The thickness of the diffusion layer can be determined by EPMA line analysis of a cross-section along the TD plane of the plate. When performing line analysis along a line parallel to the plate thickness direction on the TD plane that includes the dissimilar metal interface, starting from the first layer side or the third layer side mainly composed of nickel, as described above, as the measurement point moves to the second layer side made of an iron-based alloy, there is a region where the Ni composition gradually decreases and the Fe composition gradually increases. This region is affected by the mutual diffusion of atoms at the interface. However, for the diffusion layer of the clad plate according to the present disclosure, in mass%, it is the region between the point where the Fe composition is 10% and the point where the Ni composition is 10%. Therefore, perform the above EPMA line analysis, measure the distance between the point where the Fe composition is 10% and the point where the Ni composition is 10% at five or more different locations on the TD plane of the plate that are 10 μm or more away from the dissimilar metal interface, and take the average value of these values as the average thickness of the diffusion layer.

[0037] The identification of the Al enrichment part in the diffusion layer can be carried out by EPMA surface analysis within the above-mentioned diffusion layer. Perform surface analysis on the region of the cross-section that is the TD plane including the diffusion layer, identify all regions within a predetermined area of the diffusion layer where the Al concentration is 15% or more in mass%, and confirm whether the area exceeds the area of a circle with 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 within the diffusion layer, perform the above investigation on an area of 20 μm 2 or more and 40 μm 2 or less. If no Al enrichment part exceeding the area of a circle with a diameter of 250 nm is found at 0.50 per μm [[ID=​​​​​​It is believed that the Al contained in the nickel-containing metal material and iron-based alloy material used in the manufacture of the clad plate according to this disclosure influences the formation of the Al-enriched areas. As mentioned above, for example, both pure nickel and carbon steel inevitably contain Al that is mixed in from the raw materials or used in the refining process. When the materials that will become the clad plate are heated to join them together, an oxide film is formed when the surface of the materials reacts with the atmosphere. However, Al has the property of oxidizing even at a lower oxygen potential than Ni, the main element of nickel-containing metals, and Fe, the main element of iron-based alloys.

[0039] For example, in pure nickel and carbon steel, Ni and Fe, which are most abundant on the outermost surfaces of each material, are preferentially oxidized in the initial stages of oxidation. However, as oxidation progresses gradually from the outermost surface of each material into the interior, it is thought that an Al-containing oxide is formed when the oxygen potential decreases to a certain level. Even if the void between the nickel-containing material and the iron-based alloy material is sealed by welding or other means and the atmosphere is evacuated with a pump or the like before rolling and joining, a perfect vacuum cannot be achieved. Therefore, it is difficult to completely suppress the formation of oxides. Consequently, heating for joining results in a certain amount of Al oxide being formed on the surface of the joined material. In the process of joining the materials by rolling or other means, Al-containing oxide is incorporated into the metals of each layer near the dissimilar metal interface due to the action of plastic flow at the interface. As a result, it is thought that granularly concentrated Al-enriched areas are formed in the nickel-containing layer or the carbon steel layer near the dissimilar metal interface, i.e., in the diffusion layer.

[0040] (5) Total thickness The clad plate according to this disclosure has a total thickness of more than 0.1 mm, whether it is a two-layer structure consisting of a first and second layer, or a three-layer structure including a third layer. When the total thickness is more than 0.1 mm, it is easier to maintain the shape required for use as a material for plants. From the viewpoint of shape retention, the total thickness of the clad plate is preferably 0.2 mm or more, and more preferably 0.3 mm or more. On the other hand, considering the processability and cost when used as a material for batteries or for salt electrolysis and alkaline water electrolysis plants, the total thickness of the clad plate is 3.0 mm or less. From the viewpoint of cost, the total thickness of the clad plate is preferably 2.8 mm or less.

[0041] (6)Applications The clad plate according to this disclosure exhibits high corrosion resistance in an immersion environment in an alkaline solution, and even when bent, interfacial delamination between the nickel-containing layer, which is mainly composed of Ni, and the iron-based alloy layer is less likely to occur. The applications of the clad plate according to this disclosure are not particularly limited, and it can be suitably used, for example, as a material for batteries, a material for alkaline water electrolysis plants, a cathode material or pan material for salt electrolysis equipment used in the production of caustic soda, a basic industrial chemical. Depending on the application, the clad plate according to this disclosure can be bent to form a molded product having a desired shape.

[0042] The above explanation mainly describes the case in which the diffusion layers at both interfaces of a three-layer clad plate satisfy the requirements of this disclosure (average thickness of the diffusion layer and number density of coarse-grained Al-enriched areas). However, the clad plate according to this disclosure may also be a two-layer clad plate, or only the diffusion layer at one of the two interfaces of a three-layer clad plate may satisfy the requirements of this disclosure. When bending clad plates, delamination is particularly likely to occur in the nickel-containing layer on the outer surface of the bent portion. However, in the case of a three-layer clad plate where only the diffusion layer at the interface between the first and second layers satisfies the requirements of this disclosure, the occurrence of interface delamination can be suppressed by performing the bending process so that the first layer is on the outer surface of the bent portion.

[0043] [Method for manufacturing clad plates] Next, a preferred manufacturing method for the clad plate according to this disclosure will be described. Note that the clad plate according to this disclosure will achieve the above-mentioned effects regardless of the manufacturing method, as long as it possesses the characteristics described above. While the manufacturing method for the clad plate according to this disclosure is not limited, the following method is preferred because it allows for stable production. The clad sheet according to this disclosure can be manufactured through the following lamination, rolling and joining, cold rolling, and annealing processes. Other processes may be included, and depending on the application, for example, a descaling process to remove scale formed on the sheet surface may be performed before the cold rolling process, or it may be omitted. The following description will primarily focus on a method for manufacturing a clad plate according to this disclosure, using a three-layer clad plate in which a nickel-containing layer, an iron-based alloy layer, and another nickel-containing layer are laminated in that order as an example. However, a two-layer clad plate in which a nickel-containing layer and an iron-based alloy layer are laminated can also be manufactured using the same method. Furthermore, in some parts of the description, the nickel-containing layer is described as a layer made of pure nickel and the iron-based alloy layer as a preferred embodiment. However, a nickel-based alloy or similar material may be used for the nickel-containing layer, and stainless steel or similar material may be used for the iron-based alloy layer.

[0044] [Lamination process] The lamination process involves preparing the materials for the first, second, and third layers, laminating them in that order, and then partially joining them by welding or other means to form a laminate.

[0045] [Rolling and joining process] The rolling and joining process involves heating the temporarily joined laminate to a certain temperature and then hot-rolling it to form a jointed body in which the first, second, and third layers are integrated.

[0046] [Cold rolling process] The cold rolling process involves rolling the joined material at a cold temperature to a predetermined thickness to create a clad plate.

[0047] [Annealing process] The annealing process is a process in which a cold-rolled clad sheet is annealed at a constant temperature in order to impart workability to the clad sheet.

[0048] Furthermore, the preferred manufacturing method for the clad plate according to this disclosure includes the following steps: A lamination process is performed in which an iron-based alloy material, which is an iron-based alloy slab or plate, is laminated with 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% Ni and 0.50 mass% or less Al, with the remainder being Fe and impurities, between one or both sides of an iron-based alloy material, which is an iron-based alloy slab or plate, and a nickel-containing material, which is a nickel-based alloy slab or plate. The peripheral parts, including the longitudinal and widthwise ends, are welded and sealed to form a laminate. A rolling and joining process involves hot-rolling a laminate to join an iron-based alloy material and a nickel-containing material to form a joined body, A cold rolling process in which the joined material is cold-rolled to form a clad plate, An annealing process is performed on a clad sheet (cold-rolled clad sheet) after the cold rolling process, with the annealing temperature T (°C) and annealing time t (s) set to satisfy the following equation (1), Includes. 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 inserted between the iron-based alloy material and the nickel-containing material during the lamination process, and R (%) is the rolling ratio when the laminate is converted from its state before the rolling and joining process to a clad plate after the cold rolling process, which can be determined from equation (2) below. R(%) = 100 × (XW) / X ... (2) In equation (2), X (mm) is the thickness of the laminate before the rolling and joining process, and W (mm) is the thickness of the clad plate after the cold rolling process. The following explains each step in order.

[0049] (1)Lamination process In the lamination process, first, the materials for the first, second, and third layers are prepared. The shape should be adjusted so that when the clad plate is completed, the thickness of each layer (first, second, and third) is the predetermined value mentioned earlier. For example, hot-rolled pure nickel sheets can be used as the materials for the first and third layers, and a carbon steel slab can be used as the material for the second layer. These are then laminated in the order of the first, second, and third layers, in the thickness direction.

[0050] Before laminating each material, it is preferable to remove any deposits such as scale from the joint surfaces of each material by polishing or other means. Furthermore, it is preferable to insert (place) Fe-Ni alloy foil across the entire surface between the first and second layers, and between the second and third layers. By using Fe-Ni alloy foil as an insert material, it is possible to stably form a diffusion layer with a predetermined thickness and with fewer Al-enriched areas. The Fe-Ni alloy foil used mainly consists of Fe and Ni, and also contains impurities. Examples of impurity elements include C, O, N, B, Si, P, S, Al, Ti, Nb, Mo, Mg, Ca, Mn, Cr, Co, Cu, etc. 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. Furthermore, the thickness of the Fe-Ni alloy foil is related to the annealing process described later, but in order to stably exhibit the effects of the Fe-Ni alloy foil, it is preferable that it be 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, the alloy cost may increase, so the thickness is preferably 0.125 mm or less. More preferably, it is 0.110 mm or less.

[0051] After forming a laminate by laminating the materials in the order of the first, second, and third layers, with Fe-Ni alloy foil interposed between the first and second layers, and between the second and third layers, it is preferable to temporarily fix (weld-seal) the outer periphery of the spaces between the materials of the first, second, and third layers of the laminate by welding or other means to prevent movement of each material. Preferred welding methods include shielded metal arc welding, TIG welding, and MIG welding. In addition, during or after welding, vacuuming may be performed on the air gaps between each layer sealed by welding using a rotary pump or the like. There is no specific vacuum level required, but from the viewpoint of jointability, 5.0 × 10⁻⁶ is preferable. -1 It is preferable that the value is Pa or less.

[0052] (2) Rolling and joining process The rolling and joining process involves subjecting the laminate obtained by the above method to hot rolling to join the layers together, thereby forming a jointed body in which all layers are integrated. The heating temperature before hot rolling is sufficient for joining. To obtain sufficient bonding strength, it is preferable to heat to 900°C or higher. From the viewpoint of bonding properties, it is more preferable to heat to 950°C or higher. On the other hand, excessive increases in heating temperature lead to increased load on heating equipment and increased energy costs, so it is preferable to heat to 1350°C or lower. From the viewpoint of energy costs, it is more preferable to heat to 1300°C or lower.

[0053] Regarding the rolling pass schedule, rolling and joining can be performed without problems as long as the overall rolling rate of the schedule is within a certain range. From the viewpoint of joinability, a rolling rate of 90.0% or higher for the entire schedule is preferable. On the other hand, excessive increases in the rolling rate lead to increased load on the rolling equipment, so a rolling rate of 98.5% or lower is preferable. From the viewpoint of the load on the rolling equipment, it is more preferable to have a rolling rate of 98.4% or lower. The rolling rate can be calculated using the following formula (a). Rolling ratio (%) = 100 × (XY) / X ... (a)

[0054] Here, X (mm) is the thickness of the laminate before rolling and joining, that is, the sum of the thicknesses of the first layer material, the second layer material, and the third layer material, and Y (mm) is the thickness of the joined material after rolling and joining (sometimes referred to as clad hot-rolled sheet or hot-rolled sheet). Note that the thickness of the Fe-Ni alloy foil used as the insert is sufficiently thin compared to the thickness of each material before rolling, so the thickness of the Fe-Ni alloy foil can be ignored when calculating X.

[0055] (3) Cold rolling process For clad hot-rolled sheets joined by hot rolling, descaling is performed as needed, and then cold rolling is performed to adjust the thickness to a predetermined value for the product. Descaling before cold rolling may be omitted. In the rolling pass schedule, rolling can be performed without problems as long as the overall rolling rate of the schedule is within a certain range. Hot-rolled sheets that have gone through the rolling and joining process are too thick to be used as actual plant materials, so it is preferable to perform cold rolling of at least 30% to adjust the thickness. On the other hand, if the rolling rate is increased too much, it will lead to an increased load on the rolling equipment, so it is preferable to keep the rolling rate at 95% or less. From the viewpoint of equipment load, it is even more preferable to keep it at 94% or less.

[0056] (4) Annealing process In the cold rolling process, work hardening inevitably occurs in the clad sheet, reducing its workability. Therefore, annealing is performed to obtain sufficient workability. The annealing temperature is preferably 700°C or higher, at which point both the pure nickel layer and the carbon steel layer soften. From the viewpoint of promoting softening, it is more preferably 725°C or higher. On the other hand, excessive temperature increases lead to increased load on the annealing equipment and increased energy costs, so the annealing temperature is preferably 1150°C or lower. From the viewpoint of energy costs, it is more preferably 1100°C or lower.

[0057] The annealing temperature and annealing time in the annealing process are preferably within the range of the following formula (b). 0.010 ≦ B ≦ 0.200 (b) The value of B in equation (b) is given by equation (c) below. B=0.2958×A×R×[0.001×t×exp{-8596.1 / (T+273.15)}] 1 / 2 ··· (c) Here, A (mm) is the thickness of the Fe-Ni alloy foil inserted between the materials of the first and second layers, and between the materials of the second and third layers, R (%) is the rolling ratio (also called the total rolling ratio) when the laminate is cold-rolled from its state before rolling and joining, t (s) is the annealing time, and T (°C) is the annealing temperature. R can be calculated from the following formula (d). R(%) = 100 × (XW) / X ··· (d) Here, X (mm) is the thickness of the laminate before rolling and joining, that is, the sum of the thicknesses of the first layer material, the second layer material, and the third layer material, and W (mm) is the thickness of the clad sheet after cold rolling. Note that the thickness of the Fe-Ni alloy foil used as the insert is sufficiently thin compared to the sum of the thicknesses of each material before rolling, X, so the thickness of the Fe-Ni alloy foil can be ignored when calculating X.

[0058] In equation (b) above, if the annealing temperature and annealing time are set so that the value of B is less than 0.010, it becomes difficult to form a diffusion layer of a stable thickness. Conversely, if the annealing temperature and annealing time are set so that the value of B exceeds 0.200, the diffusion layer tends to become thicker, which may destabilize the mechanical properties of the dissimilar metal interface. Regarding the effects of inserting Fe-Ni alloy foil as described above, and the effects of controlling the rolling ratio, annealing temperature, and annealing time when forming a clad sheet after cold rolling, based on the foil thickness of the insert material and the state of the laminate before rolling and bonding, there are still many unknowns and it remains in the realm of speculation, but the following factors can be considered.

[0059] First, regarding the effect on Al-enriched areas in the diffusion layer, it is presumed that suppressing the amount of oxide generated per unit area of ​​each material in the first and second layers, and each material in the second and third layers, will have the effect of suppressing the formation of Al-enriched areas. Although there are many unknowns regarding the formation behavior of Al-containing oxides on the surface of each layer's material and Fe-Ni alloy metal foil, at least by placing metal foil in the voids between the materials, the area on which the metal reacts with the atmosphere increases, and the amount of oxygen reacting per unit surface area of ​​the metal, i.e., the degree of oxidation, decreases. By suppressing the degree of oxidation per unit surface area of ​​the metal, only the surface of each metal material is oxidized, and the oxidation reaction does not progress further into the interior. When only a small amount of oxidation occurs near the surface, similar to the initial stages of oxidation in general atmosphere, elements that readily combine with oxygen are not oxidized, but rather elements present on the surface are preferentially oxidized. In other words, it is thought that oxidation of Ni and Fe on the surface of pure nickel and carbon steel materials occurs preferentially, and Al is less likely to be oxidized.

[0060] Furthermore, regarding the effect on the thickness of the diffusion layer, it is presumed that the thickness can be controlled within a predetermined range by using an insert and performing appropriate heat treatment. If an insert is not used, pure nickel and carbon steel are in close contact and joined during the rolling bonding process, and a diffusion layer is formed during the hot rolling bonding process or the annealing process. However, the interface where pure nickel and carbon steel are joined by rolling is not necessarily flat, and the reduction is not applied uniformly, so the subsequent formation of the diffusion layer is unlikely to be uniform and is likely to be unstable.

[0061] On the other hand, by using Fe-Ni alloy foil as an insert, a layer of uniformly mixed Fe and Ni is formed in advance, which is thought to facilitate the formation of a stable diffusion layer of uniform thickness after bonding. In addition to these, in the annealing process, where the state of the diffusion layer inevitably changes, it is necessary to appropriately control the thickness distribution of the diffusion layer by appropriately adjusting the annealing conditions, especially the annealing temperature and time. The contents of equation (b) described above are empirical equations, but this equation contains parts that seem to correspond to the thickness of the Fe-Ni alloy foil inserted in the lamination process after cold rolling, and parts that seem to correspond to the diffusion distance in the annealing process. In other words, 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. Therefore, it is presumed that by controlling this equation (b) within a certain range obtained empirically, the thickness of the diffusion layer can be stably formed within the range defined by the clad plate according to this disclosure. The method for manufacturing the clad plate according to this disclosure is not limited to the method described above, and the clad plate according to this disclosure may be manufactured without using Fe-Ni alloy foil. [Examples]

[0062] The effects of this disclosure will be explained below with reference to examples, but this disclosure is not limited to the conditions used in the following examples.

[0063] Pure nickel NW2201 or nickel-based alloy NCF600 was used as the material for the first and third layers of the clad plate, and carbon steel SPCC, SPCE, or stainless steel SUS304 was used as the material for the second layer. Using these materials, a 3-layer clamshell is created by laminating the first, second, and third layers in that order. Clad plates, or two-layer clad plates with the first and second layers laminated in this order, were manufactured through the above-described lamination process, rolling and joining process, descaling process, cold rolling process, and annealing process. Some parts of the descaling process were omitted.

[0064] Furthermore, for some clad plates, during the lamination process, an Fe-Ni alloy foil containing 50% Ni by mass and the remainder being Fe and impurities was placed between the materials of the first and second layers, and between the materials of the second and third layers. In addition, for some clad plates, the Fe-Ni alloy foil was placed between the materials of the first and second layers, but not between the materials of the second and third layers. The thickness of the materials was adjusted to the thickness described later by the rolling rate in the rolling bonding process and the cold rolling process.

[0065] During the fabrication of each clad plate, the thickness A (mm) of the Fe-Ni alloy foil insert, the rolling ratio R (%) of the total thickness from the lamination process to the cold rolling process, the temperature T (°C), and the time t (s) in the annealing process were varied. Based on these values, the value of B in equation (c) was calculated. The descaling process was performed by surface grinding.

[0066] For each fabricated clad plate, EPMA linear analysis was performed along the thickness direction at five locations in the plate cross-section along the TD plane, near the dissimilar metal interfaces: at the interface between the first and second layers and the interface between the second and third layers for three-layer clad plates, and at the interface between the first and second layers for two-layer clad plates. The average thickness of the diffusion layer was measured by performing this analysis at five locations in each region. Furthermore, EPMA surface analysis was performed on each diffusion layer at 30 μm. 2 The experiment was conducted over the specified area, and the number density of granular Al-enriched regions with an equivalent circular diameter of 250 nm or more (labeled "coarse Al-enriched regions" in Table 2) was investigated. In the case of a three-layer clad plate, if the evaluation of the number density of coarse Al-enriched regions in the diffusion layers of two interfaces differed, the evaluation for each interface was recorded in Table 2.

[0067] [evaluation] <Bending Test> The bending test was performed using the press bending method in accordance with JIS Z 2248:2022. The bending test specimen had a width of 10 mm, an inner radius of 4 mm, and a support radius of 14 mm. Two bending angles were used: 45° and 90°. In all bending tests, the first layer was positioned on the outer circumference (outside) of the bent section. In the 45° bending test, if partial or complete delamination occurred at the dissimilar metal interface, it was marked as "yes" (yes), indicating failure; if no delamination occurred, it was marked as "no" (no). In the 90° bending test, if the first layer fractured and the second layer was exposed, it was marked as "yes"; if the second layer was not exposed, it was marked as "no". In the 90° bending test, even if wrinkles or cracks occurred in the first layer, if no exposure of the second layer was observed, it was marked as "no". Although the fracture of the first layer is not directly related to the problem of this disclosure, test materials judged as "no" are preferable because they offer greater flexibility in bending. Table 1 shows the material, number of layers, and manufacturing conditions for each cladding plate, while Table 2 shows the thickness, EPMA analysis, and bending test results for each cladding plate.

[0068] [Table 1]

[0069] [Table 2]

[0070] Numbers 1-9 and 12-14 are clad plates of this disclosure. As can be seen from Table 2, Nos. 1-9, 13, and 14 were found to be less prone to delamination at the dissimilar metal interface during bending tests (45° bend), and less prone to fracture of the first layer (90° bend). This confirmed that they can be suitably used as materials for applications requiring particularly large bending. Furthermore, in No. 8, the thickness of the diffusion layer and the number density of coarse Al-enriched areas at the interface between the first and second layers, which is the outer surface of the bent portion prone to delamination or fracture, were within the range of this disclosure, and no delamination or fracture occurred in either 45° or 90° bending. In sample No. 12, no delamination occurred at the interface during the 45° bending test, but the thickness of the first and third layers was thin, causing the first layer to rupture and the second layer to be exposed during the 90° bending test. In No. 14, the Al concentration in the Fe-Ni alloy foil was relatively high, resulting in a relatively high number density of coarse Al-enriched areas in the diffusion layer, although within the acceptable range. Consequently, no interfacial delamination occurred in the 45° bending test, but delamination occurred at the interface in the 90° bending test. In samples No. 10 and 11, the annealing after the rolling and joining process was insufficient, resulting in an insufficient diffusion layer thickness and delamination at the interface during the 45° bending test. In No. 15, the high Al concentration in the Fe-Ni alloy foil used resulted in a number density of coarse Al-enriched areas in the diffusion layer exceeding the upper limit of this disclosure, causing delamination at the interface in both the 45° bending test and the 90° bending test.

[0071] The disclosure of Japanese Patent Application No. 2023-072770, filed on 26 April 2023, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually described. [Explanation of Symbols]

[0072] 1. Clad plate 2. First layer (nickel-containing layer) 3. Second layer (iron-based alloy layer) 4. Third layer (nickel-containing layer)

Claims

1. It comprises an iron-based alloy layer made of an iron-based alloy, and a nickel-containing layer mainly composed of Ni, which is laminated on one or both sides of the iron-based alloy layer. The total thickness is greater than 0.1 mm and less than or equal to 3.0 mm. Between at least one side of the iron-based alloy layer and the nickel-containing layer, there exists a diffusion layer with an average thickness of 0.50 μm to 10.0 μm, in which the concentrations of Ni and Fe are both 10% by mass or more, and within the diffusion layer, in a cross-section normalized to the direction perpendicular to the rolling direction and the thickness direction, the concentration of Al is 15% by mass or more, and the number density of granular Al-enriched portions with an equivalent circle diameter of 250 nm or more is 0.50 particles / μm ２ A clad plate that is less than [a certain value].

2. The nickel-containing layer is laminated on both sides of the iron-based alloy layer, and the diffusion layer exists between both sides of the iron-based alloy layer and the nickel-containing layer, with the number density of the granular Al-enriched portion being 0.50 particles / μm² within each of the diffusion layers in the cross-section. ２ A clad plate according to claim 1, which is less than [amount missing].

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

4. A lamination process is performed in which an iron-based alloy material, which is an iron-based alloy slab or plate, is laminated with 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% Ni and 0.50 mass% or less Al, with the remainder being Fe and impurities, between one or both sides of an iron-based alloy material, which is an iron-based alloy slab or plate, and a nickel-containing material, which is a nickel-based alloy slab or plate. The peripheral portion, including the longitudinal and widthwise ends, is then welded to seal the laminate. A rolling and joining process is performed to join the iron-based alloy material and the nickel-containing material by hot rolling the laminate to form a joined body. A cold rolling process in which the joined body is cold-rolled to form a clad plate, An annealing step is performed on the clad plate after the cold rolling step, with the annealing temperature T (°C) and annealing time t (s) set to satisfy the following formula (1): A method for manufacturing a clad plate, comprising the clad plate according to any one of claims 1 to 3. 0.010 ≦ 0.2958×A×R×[0.001×t×exp{-8596.1 / (T+273.15)}] １／２ ≦ 0.200 ・・・ (1) In formula (1) above, A (mm) is the thickness of the Fe-Ni alloy foil, and R (%) is the rolling ratio when the laminate is transformed from its state before the rolling and joining process to a clad plate after the cold rolling process, which can be determined from formula (2) below. R (%) = 100×(X-W) / X... (2) In equation (2) above, X (mm) is the thickness of the laminate before the rolling and joining process, and W (mm) is the thickness of the clad plate after the cold rolling process.

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