Clad

Abstract

Clad 1 includes a first layer 2 and a third layer 4 made of pure nickel or a Ni-based alloy, and a second layer 3 made of an Fe-based alloy, in which the standard deviations s1 and s3 of the thicknesses [μm] of the first and third layers are 60 [μm] or less, respectively, and the clad 1 satisfies the following formula: 0.050≦(t1×d1×[Ni]1+t2×d2×[Ni]2+t3×d3×[Ni]3) / (t1×d1+t2×d2+t3×d3)≦0.630 t1, t2, and t3 are the ratios of the thickness of the first, second, and third layers when the total thickness of the cladding is 1, and d1, d2, and d3 are the densities of the first, second, and third layers [g / cm 3 ], [Ni]1, [Ni]2, and [Ni]3 are the mass ratios of Ni per unit mass of the first, second, and third layers. The clad may be composed of the first and second layers.

Description

[Technical Field]

[0001] The present disclosure relates to cladding. [Background technology]

[0002] Nickel sheet and Ni-based alloy sheet are used in chemical plants that handle alkaline solutions, as electrode materials for secondary batteries used in the electrification technology of various industrial products, such as electric vehicles, and as hydrogen storage alloys used in hydrogen transportation, etc. These products are particularly essential for realizing a carbon-neutral society that will curb climate change caused by greenhouse gases, such as carbon dioxide, and demand for nickel bullion used in these products is expected to increase further in the future. In addition, due to the influence of changes in the global balance of supply and demand for nickel ore, the price of nickel bullion tends to fluctuate dramatically, so there is a demand for materials that can reduce the amount of nickel bullion used while taking advantage of the properties of nickel.

[0003] Pure nickel (Ni) and some Ni-based alloys (in this disclosure, pure nickel and Ni-based alloys may be collectively referred to as "Ni-based metals") have extremely high corrosion resistance in certain environments, such as alkaline environments. Therefore, in environments where Ni-based metals exhibit corrosion-resistant behavior, thinning during use is unlikely to be a problem. For this reason, when using Ni-based metals, it is possible to reduce material costs by using a general-purpose, inexpensive metal material for the inner layer and substituting a plate material with a Ni-based metal of a certain thickness or greater for the outer layer.

[0004] As a method for manufacturing such a plate material having a multi-layer structure, for example, there is a technique in which nickel plating is applied to the surface of carbon steel, which is a general-purpose metal. For example, 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 Ni-Fe diffusion layer, with the proportion of exposed iron at the outermost surface of the nickel plating layer being 30% or less. This nickel plating can be achieved by forming a nickel plating layer on one or both sides of a carbon steel sheet by electrolytic plating or electroless plating using a catalyst, and optionally performing a post-plating heat treatment or the like. Because the thickness of the plating layer in such a plated multilayer material is thinner than the thickness of the steel sheet or other substrate, the amount of Ni used can be reduced. However, because the plating layer is thin, if bending is required for use as a plant component, for example, the plating layer may break at the outer periphery of the bend, exposing the Fe in the carbon steel, which could result in a local decrease in corrosion resistance. Meanwhile, increasing the thickness of the plating layer is generally difficult and inefficient.

[0005] Another example of a multi-layer material is a clad material (sometimes simply referred to as "clad") in which a clad material that imparts new functionality is bonded to the surface of a base material made of a general-purpose metal. For example, Patent Document 2 discloses a method of obtaining a clad by hot rolling an assembled material obtained by overlapping a set of a base material made of carbon steel and a clad material made of one of stainless steel, pure nickel, and a Ni-based alloy and welding the peripheral portions.

[0006] Patent document 1: Japanese Patent Application Laid-Open No. 6-2104 Patent document 2: Japanese Patent Application Laid-Open No. 192404 / 1999

[0007] Non-patent document 1: Sakaki Takashi, Shimizu Kaname, Tosoh Research Report, Vol. 33, No. 1, (1989), pp. 45-55 Summary of the Invention [Problem to be solved by the invention]

[0008] The nickel-clad steels specified in Patent Document 2 and JIS G 3602:2012 are thick, and the JIS specification only specifies that the thickness of the outer nickel layer of the cladding material must be 1 mm or more, less than 5 mm, or 5 mm or more. Regarding clads, the manufacturing and usage issues common to thick and thin plate materials, as well as the manufacturing and usage issues specific to thin plate materials, have not been taken into consideration.

[0009] In industrial product components exposed to alkaline environments, nickel plates are expected to undergo not only bending but also welding and other processes. For example, when a clad plate made of nickel clad with carbon steel as the base material is used as a substitute for nickel plates, depending on the welding conditions, the internal carbon steel base material may become exposed, which may result in a local decrease in alkaline corrosion resistance. Furthermore, when welding clad plates, Fe may be locally exposed in the weld metal portion (in this disclosure, "weld metal portion" refers to the "weld bead"), which may result in a decrease in alkaline corrosion resistance. In particular, there are cases where almost the entire weld metal portion has low corrosion resistance, and cases where the weld metal portion contains a mixture of high and low corrosion resistance areas.

[0010] The present disclosure has been made in view of the above-mentioned problems. That is, an object of the present disclosure is to provide a cladding that can keep material costs low and ensures corrosion resistance of the welded metal part in an alkaline environment even after welding. [Means for solving the problem]

[0011] The above problems can be solved by the following means. <1> a two-layer structure including a first layer made of pure nickel or a Ni-based alloy and a second layer made of an Fe-based alloy and bonded to one surface of the first layer, or a three-layer structure further including a third layer made of pure nickel or a Ni-based alloy and bonded to the surface of the second layer opposite to the surface bonded to the first layer, When the standard deviation of the thickness [μm] of the first layer is s1 and the standard deviation of the thickness [μm] of the third layer is s3, s1 and s3 are each 60 [μm] or less, A clad that satisfies the following formula (I): 0.050≦(t1×d1×[Ni]1+t2×d2×[Ni]2+t3×d3×[Ni]3) / (t1×d1+t2×d2+t3×d3)≦0.630 Formula (I) In the formula (I), t1 is the ratio of the average thickness of the first layer when the average total thickness of the cladding is 1, t2 is the ratio of the average thickness of the second layer when the average total thickness of the cladding is 1, t3 is the ratio of the average thickness of the third layer when the average total thickness of the cladding is 1, and d1 is the density [g / cm 3 ], d2 is the density of the second layer [g / cm 3 ], d3 is the density of the third layer [g / cm 3 ], [Ni]1 is the mass fraction of Ni per unit mass of the first layer, [Ni]2 is the mass fraction of Ni per unit mass of the second layer, and [Ni]3 is the mass fraction of Ni per unit mass of the third layer. However, in the case of the two-layer structure, t3, d3, and [Ni]3 are each set to 0 in the formula (I). <2> The two-layer structure is such that the average thickness of the first layer is 30 μm or more and 300 μm or less. <1> The cladding according to claim 1. <3> The two-layer structure is such that the first layer is pure nickel. <1> or <2> The cladding according to claim 1. <4> The three-layer structure is provided, and the average thickness of at least one of the first layer and the third layer is 30 μm or more and 300 μm or less. <1> The cladding according to claim 1. <5> The three-layer structure is provided, and at least one of the first layer and the third layer is made of pure nickel. <1> or <4> The cladding according to claim 1. <6> The average total thickness is more than 0.1 mm and 3.0 mm or less; <1> ~ <5> The clad according to any one of the above. [Effects of the Invention]

[0012] According to the present disclosure, a clad is provided that can keep material costs low and ensures corrosion resistance of the weld metal portion in an alkaline environment even when welding is performed. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram showing the overall configuration of a clad having a three-layer structure, which is an example of a clad according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment that is an example of the present disclosure will be described. In this disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. However, when the numerical values ​​written before and after "to" are followed by "greater than" or "less than," the numerical range does not include these numerical values ​​as the lower or upper limit. The content of an element in a chemical composition may be expressed by adding "amount" to the element symbol (for example, C amount, Si amount, etc.). With respect to the content of elements in the chemical composition, "%" means "mass %." When the content of an element in the chemical composition is stated as "0~", it means that the element does not have to be contained. The term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0015] As a result of extensive research into solving the above problems, the present inventors have made the following findings. (A) When a clad made of an Fe-based alloy such as carbon steel as the base material and a Ni-based metal as the cladding material is joined to another component by welding, the base material layer of the clad may partially melt, exposing Fe in the molten metal. (B) In the weld metal part of a thin clad plate with a base material of an Fe-based alloy such as carbon steel and a clad material of an Ni-based metal, the components of the Fe-based alloy and the Ni-based metal mix when melted, and although it is possible that an intermetallic compound may be formed, it is expected that the weld metal will basically be an alloy with Ni and Fe as the main components. (C) As shown in Non-Patent Document 1, it is expected that in an alkaline environment, an alloy whose main components are Ni and Fe will have improved corrosion resistance and ensure sufficient corrosion resistance if it contains more than a certain amount of Ni. For this reason, to ensure the corrosion resistance of the weld metal zone, the Ni concentration in the weld metal zone must be more than a certain amount. (D) Welding conditions vary depending on the application, product, or welding operator, and there is a possibility that the condition of the weld metal, especially its Ni concentration, may vary greatly. For this reason, regardless of the welding conditions under which the clad is welded, the Ni content in the weld metal must be as stable as possible and be at a certain level or higher. (E) When welding using welding materials such as welding rods and welding wires, the concentration of Ni in the weld metal is affected by the components in the welding material, but it is thought that most of the concentration varies depending on the Ni concentration in the cladding layer made of Ni-based metal and the value of the cladding layer's thickness relative to the total thickness. For this reason, by creating a cladding in which the Ni concentration in the cladding layer made of Ni-based metal and the value of the cladding layer's thickness relative to the total thickness are within a certain range, it is possible to maintain the Ni content in the weld metal at a certain level or higher, regardless of the welding method. (F) Depending on the manufacturing method, the thickness of the clad cladding layer may vary significantly from one part of the plate to another. In areas where the clad cladding layer is thin, the Ni concentration derived from the clad material in the weld metal may be excessively low. On the other hand, clad cladding with locally thick clad layer thicknesses ends up using more nickel base metal than necessary, making it difficult to achieve cost reductions. For this reason, it is preferable that the deviation in clad layer thickness within a thin clad plate be within a certain range.

[0016] The clad according to the present disclosure was created based on the above findings. That is, the clad according to the present disclosure has a two-layer structure including a first layer made of pure nickel or a Ni-based alloy and a second layer made of an Fe-based alloy bonded to one surface of the first layer, or a three-layer structure further including a third layer made of pure nickel or a Ni-based alloy bonded to the surface of the second layer opposite to the surface bonded to the first layer. When the standard deviation of the thickness [μm] of the first layer is s1 and the standard deviation of the thickness [μm] of the third layer is s3, s1 and s3 are each 60 [μm] or less and satisfy the following formula (I). 0.050≦(t1×d1×[Ni]1+t2×d2×[Ni]2+t3×d3×[Ni]3) / (t1×d1+t2×d2+t3×d3)≦0.630 Formula (I) In formula (I), t1 is the ratio of the average thickness of the first layer when the average total thickness of the cladding is 1, t2 is the ratio of the average thickness of the second layer when the average total thickness of the cladding is 1, t3 is the ratio of the average thickness of the third layer when the average total thickness of the cladding is 1, and d1 is the density of the first layer [g / cm 3 ], d2 is the density of the second layer [g / cm 3 ], d3 is the density of the third layer [g / cm 3 ], [Ni]1 is the mass fraction of Ni per unit mass of the first layer, [Ni]2 is the mass fraction of Ni per unit mass of the second layer, and [Ni]3 is the mass fraction of Ni per unit mass of the third layer. However, in the case of a two-layer structure, t3, d3, and [Ni]3 are each set to 0 in the formula (I). In the following description, the term "main component" refers to the element that is contained in the largest amount (mass %), preferably 50% or more, among the elements that make up the metal material.

[0017] 1. Cladding according to the present disclosure (1) Overall structure The cladding according to the present disclosure has a two-layer structure or a three-layer structure. FIG. 1 is a schematic diagram showing the overall configuration of a three-layer cladding, which is an example of a cladding according to the present disclosure (in this disclosure, a two-layer cladding may be referred to as a "two-layer cladding" and a three-layer cladding may be referred to as a "three-layer cladding"). As shown in FIG. 1, the three-layer cladding 1 comprises a first layer 2, a second layer 3, and an optional third layer 4. The first layer 2 is bonded to one of the two surfaces of the second layer 3, and the third layer 4 is bonded to the other surface (i.e., the surface of the second layer 3 opposite to the surface bonded to the first layer 2). The following explanation will mainly focus on the three-layer cladding. Note that a two-layer cladding is similar to the three-layer cladding 1, except that it is composed of the first layer 2 and the second layer 3 and does not have the third layer 4.

[0018] (2) 1st and 3rd layers The first layer 2 and the third layer 4 are made of a Ni-based metal containing Ni as the main component. The type of Ni-based metal is not particularly specified, but representative examples include various Ni-based alloys as described in JIS G 4902:2019, pure nickel, etc. From the viewpoint of corrosion resistance, the use of pure nickel is preferred.

[0019] Representative examples of Ni-based alloys include NCF600, NCF601, NCF625, NCF690, NCF718, NCF750, and NCF751, as described in JIS G 4902:2019. Representative examples of pure nickel include NW2200 and NW2201, as described in JIS G 4902:2019. These Ni-based alloys and pure nickel contain Ni as the main component and may contain, for example, C, O, N, B, Si, Mn, P, S, Al, Ti, Nb, Mo, Mg, Ca, Cr, Co, Cu, and Fe as alloying or impurity elements. Pure nickel preferably contains 98% or more Ni by mass, and more preferably 99% or more Ni, as an elemental composition.

[0020] When the standard deviation of the thickness of the first layer of the cladding according to the present disclosure is s1 and the standard deviation of the thickness of the third layer is s3, s1 and s3 are each 60 μm or less. The clad is joined via a weld metal portion during welding. The weld metal portion is believed to contain Ni, primarily derived from the Ni-based metal of the first and third cladding layers. The corrosion resistance of the weld metal portion in an alkaline environment is believed to be affected by the amount of Ni contained in the weld metal portion. The clad according to the present disclosure can ensure sufficient corrosion resistance of the weld metal portion in an alkaline environment after welding by setting the thickness configuration of each layer within an appropriate range, as described below. When setting this thickness configuration, the thickness distribution of the first layer and the third layer, i.e., the standard deviation, is important. In a multilayer material such as a clad, variations in the thickness of each layer from location to location inevitably occur due to the manufacturing process. The thickness configuration of each layer constituting the clad at each location affects the variation in corrosion resistance in an alkaline environment of the weld metal portion formed during welding at that location, so it is preferable to minimize the variation in thickness from location to location in the clad. For this reason, the standard deviation of the thickness of the first and third layers of the clad according to the present disclosure is 60 μm or less. From the viewpoint of ensuring corrosion resistance of the weld metal portion in an alkaline environment throughout the cladding, the thickness is preferably 55 μm or less, more preferably 50 μm or less, and even more preferably 45 μm or less. Here, the standard deviation is the square root of the mean square of the difference between the thickness of each layer measured at each location and the average value, and is expressed by the following formula (II).

[0021]

number

[0022] where s is the standard deviation, n is the number of measurement points for the layer thickness, and x i is the layer thickness measured at the i-th location among all n locations of the layer thickness, and x ave is the average layer thickness of all n measurement points.

[0023] The average thickness of the first layer and the average thickness of the third layer of the clad according to the present disclosure are preferably 30 μm or more and 300 μm or less, respectively. If the first and third layers made of pure nickel or a Ni-based alloy are too thin, the layer on the outer periphery of the bend may break during severe bending, exposing the Fe-based alloy base material, which may result in a decrease in corrosion resistance. Furthermore, when welding is performed, the corrosion resistance of the weld metal may be decreased. Therefore, the average thickness of the first and third layers is preferably 30 μm or more. From the viewpoint of ensuring the corrosion resistance of the weld metal, it is more preferably 40 μm or more, and even more preferably 50 μm or more.

[0024] On the other hand, if the first layer and the third layer are made too thick, the material costs will increase more than necessary, so the average thickness of each of the first layer and the third layer is preferably 300 μm or less. From the viewpoint of cost, the average thickness of each of the first layer and the third layer is more preferably 275 μm or less, and even more preferably 250 μm or less. The average thickness of the first layer and the third layer may be the same, or may be different depending on the application. The method for measuring the standard deviation and average thickness of each layer is to prepare a plate cross-section observation sample at 10 different locations on the clad, each at least 50 mm apart, with the observation surface being a plane parallel to the rolling direction and thickness direction (L cross-section). Within that field of view, the thickness of the first layer and the thickness of the third layer are measured at 10 points per observation sample, and the standard deviation and average thickness are calculated by arithmetic mean from the obtained data on each layer thickness for 100 points. The cross section of the clad is polished and measured using an optical microscope at a magnification of 50. The iron-based alloy and Ni-based alloy parts can be distinguished without etching, but if this is difficult to distinguish, the cross section can be polished, then etched with nital to measure the thickness of each layer.

[0025] (3)Second layer The second layer is made of an Fe-based alloy containing Fe as a main component. The Fe-based alloy preferably has an Fe content of 50%, and may have an Fe content of 60% or more, 70% or more, 80% or more by mass, or 90% or more by mass. The type of Fe-based alloy is not particularly limited, but examples thereof include carbon steel, stainless steel, nickel steel, nickel-chromium steel, nickel-chromium-molybdenum steel, chromium steel, chromium-molybdenum steel, and manganese steel. From the viewpoint of cost, carbon steel is preferably used. Examples of the type of carbon steel that can be used include SPCC, SPCD, SPCE, SPCF, and SPCG as specified in JIS G 3141:2021.

[0026] The Fe-based alloy constituting the second layer may have a chemical composition, by mass%, of 1.0% or less of C, 1.0% or less of Si, 3.0% or less of Mn, 0.05% or less of P, 0.03% or less of S, 1.0% or less of Al, 0.3% or less of Ti, 0.01% or less of B, 0.05% or less of N, 1.0% or less of Mo, 2.0% or less of Cr, 3.0% or less of Ni, 3.0% or less of Cu, 0.5% or less of Nb, 0.7% or less of V, 0.01% or less of Ca, 0.01% or less of Mg, 0.01% or less of O, 0.01% or less of Ta, 1.0% or less of W, and 0.1% or less of REM. The remainder is Fe and impurities. The function and content of each of the above elements will be described below.

[0027] C: 1.0% or less C dissolves in Fe-based alloys as an interstitial element, improving the strength of the alloy as a solid-solution strengthening element. It also forms carbides with Fe, Cr, Ti, Nb, etc., contributing to precipitation strengthening. Therefore, adding an appropriate amount of C contributes to improving the strength of the clad. On the other hand, excessive C addition may lead to a decrease in the ductility and workability of the clad. Therefore, the C content is preferably 1.0% or less. From the viewpoint of workability, the C content is more preferably 0.5% or less, even more preferably 0.3% or less, and most preferably less than 0.1%. Since the effects of the clad according to the present disclosure are sufficiently exhibited even at low C contents, no lower limit is particularly set. However, if the C content is less than 0.001%, the manufacturing costs associated with decarbonization will increase significantly. For this reason, the C content is preferably 0.001% or more. From the viewpoint of manufacturing costs, the C content is more preferably 0.002% or more, even more preferably 0.005% or more.

[0028] Si: 1.0% or less Si is an effective deoxidizing element during the refining of Fe-based alloys. Si also has the effect of increasing the strength of Fe-based alloys at room temperature and at high temperatures. Therefore, if these effects are required depending on the application, Si can be added to Fe-based alloys. On the other hand, excessive addition of Si may lead to a decrease in the ductility and workability of the clad. Therefore, the Si content is preferably 1.0% or less. From the viewpoint of workability, it is more preferably less than 0.6%, and even more preferably less than 0.3%. Since even a low Si content sufficiently exhibits the effects of the clad according to the present disclosure, no lower limit is particularly set. However, since Si is an element useful in the deoxidation process of Fe-based alloys, the Si content is preferably 0.0001% or more. From the viewpoint of deoxidation of Fe-based alloys, it is more preferably 0.0002% or more, and even more preferably 0.0005% or more.

[0029] Mn:3.0% or less Like Si, Mn is an effective deoxidizing element during the refining of Fe-based alloys. Furthermore, as a solid-solution strengthening element, it improves the strength of Fe-based alloys. Furthermore, because Mn can be mixed in from raw scrap, excessively suppressing the Mn content necessitates reducing the use of scrap as a raw material during the refining of Fe-based alloys. This is undesirable from the perspective of resource circulation of metal resources. From these perspectives, a certain amount of Mn may be present. On the other hand, excessive Mn addition may lead to a decrease in the ductility and workability of the clad. Therefore, the Mn content is preferably 3.0% or less. From the perspective of workability, the Mn content is more preferably 1.5% or less, even more preferably less than 1.0%, and most preferably less than 0.5%. Since even a low Mn content sufficiently exhibits the effects of the clad according to the present disclosure, no lower limit is specifically set. However, an excessively low Mn content reduces the flexibility of scrap utilization, so the Mn content is preferably 0.001% or more. From the viewpoint of utilizing scrap, the content is more preferably 0.01% or more, even more preferably 0.03% or more, and most preferably 0.05% or more.

[0030] P:0.05% or less P is an impurity element contained in ferrochrome, which is a raw material for Fe-based alloys. Because P may reduce the hot workability and toughness of Fe-based alloys, the P content is preferably 0.05% or less. From the viewpoint of hot workability and toughness, it is more preferably 0.03% or less, and even more preferably 0.02% or less. Since a lower P content is preferable, no particular lower limit is set. However, dephosphorization during refining of Fe-based alloys is difficult, and in order to reduce the P content, it is necessary to use ferrochrome with a low P concentration as a raw material. Because ferrochrome with a low P concentration is expensive, attempting to reduce the P content more than necessary increases costs. Therefore, the P content is preferably 0.0001% or more. From the viewpoint of cost, it is more preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0031] S: 0.03% or less S is an impurity element contained in raw material scrap and the like. Since S may reduce hot workability and corrosion resistance, the S content is preferably 0.03% or less. From the viewpoint of hot workability, it is more preferably 0.02% or less, even more preferably 0.01% or less, and most preferably 0.005% or less. Since a lower S content is preferable, no lower limit is particularly set. However, if the S content is reduced more than necessary, the desulfurization load during refining of the Fe-based alloy increases, resulting in increased production costs. Therefore, the S content is preferably 0.00001% or more, and from the viewpoint of production costs, it is more preferably 0.00005% or more, even more preferably 0.0001% or more, and most preferably 0.0003% or more.

[0032] Al: 1.0% or less Like Si and Mn, Al is an effective deoxidizing element during the refining of Fe-based alloys. However, excessive Al content may result in reduced workability at room temperature. For this reason, the Al content is preferably 1.0% or less. From the viewpoint of workability, it is more preferably 0.5% or less, even more preferably 0.3% or less, and most preferably 0.1% or less. Since even a low Al content sufficiently exhibits the effects of the clad according to the present disclosure, no lower limit is specifically set. However, Al is one of the important deoxidizing elements, and if it is not used, there is a risk of losing flexibility in the deoxidation process of Fe-based alloys. Therefore, the Al content is preferably 0.001% or more. From the viewpoint of deoxidation of Fe-based alloys, it is more preferably 0.003% or more, even more preferably 0.005% or more, and most preferably 0.01% or more.

[0033] Ti: 0.5% or less Ti contributes to solid-solution strengthening of Fe-based alloys. Furthermore, when Fe-based alloys contain C, N, or the like, some of the Ti reacts with C or N to form carbides, nitrides, or the like, thereby contributing to precipitation strengthening. On the other hand, excessive Ti content may significantly reduce hot workability and cold workability. For this reason, the Ti content is preferably 0.5% or less. From the viewpoint of hot workability, it is more preferably 0.3% or less, even more preferably 0.1% or less, and most preferably 0.05% or less. Since even a low Ti content sufficiently exhibits the effects of the clad according to the present disclosure, no lower limit is particularly set. However, when strength is required depending on the application of the clad and Ti is utilized, the Ti content is preferably 0.0005% or more. From the viewpoint of ensuring strength, it is more preferably 0.001% or more.

[0034] B: 0.01% or less B has the effect of improving the hot workability of Fe-based alloys and enhancing manufacturability. On the other hand, excessive addition not only leads to a decrease in toughness, but also causes significant grain boundary segregation of B, which may conversely reduce hot workability. For this reason, the B content is preferably 0.01% or less. From the viewpoint of hot workability, it is more preferably 0.005% or less, and even more preferably 0.003% or less. Since even a low B content sufficiently exhibits the effects of the clad according to the present disclosure, no lower limit is particularly set. However, since the addition of an appropriate amount improves hot workability during manufacturing, the addition of 0.0001% or more is preferable. It is more preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0035] N: 0.05% or less Like C, N dissolves in Fe-based alloys as an interstitial element, improving the strength of the Fe-based alloy as a solid-solution strengthening element. It also forms nitrides with Fe, Cr, Ti, Nb, etc., contributing to precipitation strengthening. Therefore, adding an appropriate amount of N contributes to improving the strength of the clad. On the other hand, adding too much N may lead to a decrease in the ductility and workability of the clad. Therefore, the N content is preferably 0.05% or less. From the viewpoint of workability, it is more preferably 0.03% or less, and even more preferably 0.01% or less. Since even a low N content sufficiently exhibits the effects of the clad according to the present disclosure, no lower limit is particularly set. However, strength is required depending on the application of the clad, and when N is utilized, the N content is preferably 0.0001% or more. From the viewpoint of ensuring strength, it is more preferably 0.0005%, and even more preferably 0.001% or more.

[0036] Mo: 1.0% or less Mo enhances the corrosion resistance of Fe-based alloys and also improves their strength by forming a solid solution. However, excessive addition of Mo may reduce the ductility and workability of Fe-based alloys. For this reason, the Mo content is preferably 1.0% or less. From the viewpoint of workability, it is more preferably 0.75% or less, even more preferably 0.5% or less, and most preferably 0.3% or less. Since even a low Mo content sufficiently exhibits the effects of the clad according to the present disclosure, no lower limit is particularly set. However, strength is required depending on the application of the clad, and when Mo is utilized, the Mo content is preferably 0.01% or more. From the viewpoint of ensuring strength, it is more preferably 0.03% or more, and even more preferably 0.05% or more.

[0037] Cr:2.0% or less Cr has the effect of improving the hardenability of Fe-based alloys and also improves strength by forming a solid solution. However, excessive addition of Cr increases alloy costs and may reduce ductility and workability. For this reason, the Cr content is preferably 2.0% or less. From the viewpoints of workability and cost, it is more preferably 1.5% or less, even more preferably 1.0% or less, and most preferably 0.5% or less. Since the effects of the clad according to the present disclosure are sufficiently exhibited even at low Cr contents, no particular lower limit is set. However, when strength is required depending on the application of the clad and Cr is utilized, the Cr content is preferably 0.005% or more. From the viewpoint of ensuring strength, it is more preferably 0.01% or more, and even more preferably 0.02% or more.

[0038] Ni: 3.0% or less Ni improves the corrosion resistance and delayed fracture resistance of Fe-based alloys, and at the same time, improves strength by dissolving in solid solution. However, excessive addition may increase alloy costs and reduce ductility and workability. For this reason, the Ni content is preferably 3.0% or less. From the viewpoints of workability and cost, it is more preferably 2.0% or less, and even more preferably 1.0% or less. Since even a low Ni content sufficiently exhibits the effects of the clad according to the present disclosure, no lower limit is particularly set. However, depending on the application of the clad, strength or the corrosion resistance and delayed fracture resistance of the Fe-based alloy are required, and when Ni is used, the Ni content is preferably 0.01% or more. From the viewpoint of ensuring strength, it is more preferably 0.02% or more.

[0039] Cu:3.0% or less Cu improves the strength, particularly high-temperature strength, of Fe-based alloys, mainly through precipitation strengthening. On the other hand, excessive addition may reduce the ductility of Fe-based alloys. For this reason, the Cu content is preferably 3.0% or less. From the viewpoint of ensuring ductility, it is more preferably 2.0% or less, and even more preferably 1.0% or less. Since even a low Cu content sufficiently exhibits the effects of the clad according to the present disclosure, no lower limit is particularly set. However, strength is required depending on the application of the clad, and when Cu is utilized, the Cu content is preferably 0.01% or more. From the viewpoint of ensuring strength, it is more preferably 0.02% or more, and even more preferably 0.05% or more.

[0040] Nb: 0.5% or less Nb contributes to solid-solution strengthening of Fe-based alloys. Furthermore, when Fe-based alloys contain C, N, or the like, some of Nb reacts with C or N to form carbides, nitrides, or the like, thereby contributing to precipitation strengthening. On the other hand, excessive Nb content may significantly reduce hot workability and cold workability. For this reason, the Nb content is preferably 0.5% or less. From the viewpoint of hot workability, the Nb content is more preferably 0.3% or less, even more preferably 0.1% or less, and most preferably 0.05% or less. Since even a low Nb content sufficiently exhibits the effects of the cladding according to the present disclosure, no lower limit is particularly set. However, strength is required depending on the application of the cladding, and when Nb is utilized, the Nb content is preferably 0.0005% or more. From the viewpoint of ensuring strength, the Nb content is more preferably 0.001% or more.

[0041] V: 0.7% or less V contributes to solid-solution strengthening of Fe-based alloys. Furthermore, when Fe-based alloys contain C, N, or the like, some of V reacts with C or N to form carbides, nitrides, or the like, thereby contributing to precipitation strengthening. On the other hand, excessive V content may significantly reduce hot workability and cold workability. For this reason, the V content is preferably 0.7% or less. From the viewpoint of hot workability, it is more preferably 0.5% or less, even more preferably 0.3% or less, and most preferably 0.1% or less. Since the effects of the cladding according to the present disclosure are sufficiently exhibited even at low V contents, no lower limit is particularly set. However, strength is required depending on the application of the cladding, and when V is utilized, the V content is preferably 0.0005% or more. From the viewpoint of ensuring strength, it is more preferably 0.001% or more.

[0042] Ca: 0.01% or less Ca is an effective desulfurizing element during the refining of Fe-based alloys, and has the effect of improving hot workability and increasing manufacturability. On the other hand, an excessive Ca content impairs hot workability. For this reason, the Ca content is preferably 0.01% or less. From the viewpoint of hot workability, it is more preferably 0.007% or less, even more preferably 0.005% or less, and most preferably 0.003% or less. Since even a low Ca content sufficiently exhibits the effect of the clad according to the present disclosure, no lower limit is particularly set. However, when Ca is used to obtain the effect of desulfurization during refining, the Ca content is preferably 0.00005% or more. From the viewpoint of the desulfurization effect, it is more preferably 0.00007% or more, even more preferably 0.0001% or more.

[0043] Mg: 0.01% or less Like Ca, Mg is an effective desulfurizing element during the refining of Fe-based alloys, improving hot workability and manufacturability. On the other hand, excessive Mg content adversely impairs hot workability. For this reason, the Mg content is preferably 0.01% or less. From the viewpoint of hot workability, the Mg content is more preferably 0.007% or less, even more preferably 0.005% or less, and most preferably 0.003% or less. Since even a low Mg content sufficiently exhibits the effects of the cladding according to the present disclosure, no lower limit is particularly set. However, when Mg is used to obtain the desulfurization effect during refining, the Mg content is preferably 0.00005% or more. From the viewpoint of the desulfurization effect, the Mg content is more preferably 0.00007% or more, even more preferably 0.0001% or more.

[0044] O: 0.01% or less O is an element that may be unavoidably contained, and may impair the workability of the clad by forming oxides. Therefore, the O content is preferably 0.01% or less. From the viewpoint of ensuring workability, it is more preferably 0.007% or less, and even more preferably 0.005% or less. Since a lower O content is preferable, no particular lower limit is set. However, if the O content is reduced more than necessary, deoxidation during refining of the Fe-based alloy becomes difficult, increasing production costs. Therefore, the O content is preferably 0.00001% or more. From the viewpoint of production costs, it is more preferably 0.00002% or more, even more preferably 0.00005% or more, and most preferably 0.0001% or more.

[0045] Ta: 0.5% or less Ta contributes to solid-solution strengthening of Fe-based alloys. Furthermore, when Fe-based alloys contain C, N, or the like, some of the Ta reacts with C or N to form carbides, nitrides, or the like, thereby contributing to precipitation strengthening. On the other hand, excessive Ta content may significantly reduce hot workability and cold workability. For this reason, the Ta content is preferably 0.5% or less. From the viewpoint of hot workability, it is more preferably 0.3% or less, even more preferably 0.1% or less, and most preferably 0.05% or less. Since the effects of the clad according to the present disclosure are sufficiently exhibited even at low Ta contents, no lower limit is particularly set. However, when strength is required depending on the application of the clad and Ta is utilized, the Ta content is preferably 0.0005% or more. From the viewpoint of ensuring strength, it is more preferably 0.001% or more.

[0046] W: 1.0% or less Like Mo, W improves the corrosion resistance of Fe-based alloys and also improves their strength by dissolving in solid solution. However, excessive addition of W may reduce the ductility and workability of Fe-based alloys. For this reason, the W content is preferably 1.0% or less. From the viewpoint of workability, it is more preferably 0.75% or less, even more preferably 0.5% or less, and most preferably 0.3% or less. Since the effects of the clad according to the present disclosure are sufficiently exhibited even at low W contents, no particular lower limit is set. However, strength is required depending on the application of the clad, and when W is utilized, the W content is preferably 0.005% or more. From the viewpoint of ensuring strength, it is more preferably 0.01% or more, even more preferably 0.03% or more, and most preferably 0.05% or more.

[0047] REM: 0.1% or less REM (rare earth elements) improve the hot workability of Fe-based alloys. They also improve the corrosion resistance of Fe-based alloys. On the other hand, excessive REM content may actually reduce hot workability. For this reason, the REM content is preferably 0.1% or less. From the viewpoint of hot workability, it is more preferably 0.07% or less, and even more preferably 0.05% or less. Since even a low REM content sufficiently exhibits the effects of the cladding according to the present disclosure, no lower limit is specifically set. However, when REM is utilized to improve the hot workability of Fe-based alloys, the REM content is preferably 0.00001% or more. From the viewpoint of improving hot workability, it is more preferably 0.00005% or more, even more preferably 0.0001% or more, and most preferably 0.0005% or more. REM refers to a total of 17 elements, including Sc, Y, and lanthanides, and the REM content refers to the total content of these elements. In industry, REM is often added in the form of misch metal.

[0048] Remainder: Fe and impurities The remainder is composed of Fe and impurities. Examples of impurities include those contained in raw materials for Fe-based alloys, such as ores and scraps, and those contained in the manufacturing process. Examples include Zn, Sn, Hf, Zr, and Co.

[0049] (4) Total cladding thickness The average total thickness of the clad according to the present disclosure is preferably greater than 0.1 mm and not greater than 3.0 mm. When the clad according to the present disclosure is used as a replacement for pure nickel thin plate that has traditionally been used in applications such as plants and batteries, it is necessary for the clad to have equivalent corrosion resistance, mechanical properties, and workability. Furthermore, conventionally manufactured clad thick plate may have dimensional problems when used to replace pure nickel thin plate. For this reason, the average total thickness of the clad is preferably not greater than 3.0 mm. From the viewpoint of ensuring workability, particularly bendability, it is more preferably not greater than 2.75 mm, and even more preferably not greater than 2.5 mm. On the other hand, if the thickness is too small, it may be difficult to maintain the structure depending on the application. For this reason, it is preferable that the average total thickness of the clad is more than 0.1 mm. From the viewpoint of maintaining the structure as a mechanical component, it is more preferably 0.15 mm or more, even more preferably 0.2 mm or more, and most preferably 0.25 mm or more. The average total thickness of the clad is measured by measuring it with a micrometer at 10 different locations on the product that are at least 50 mm apart from each other, and calculating the average of the measured values.

[0050] (5) Relationship between the Ni mass fraction in the first and third layers and the total thickness ratio of each clad layer The cladding according to the present disclosure satisfies the following formula 1 when it is a two-layer cladding consisting of the first and second layers. 0.050≦(t1×d1×[Ni]1+t2×d2×[Ni]2) / (t1×d1+t2×d2)≦0.630 Formula 1 In the case of a three-layer clad consisting of the first layer, the second layer, and a third layer, the following formula 2 is satisfied. 0.050≦(t1×d1×[Ni]1+t2×d2×[Ni]2+t3×d3×[Ni]3) / (t1×d1+t2×d2+t3×d3)≦0.630 Formula 2 where t1 is the ratio of the average thickness of the first layer when the average total thickness of the cladding is 1, t2 is the ratio of the average thickness of the second layer when the average total thickness of the cladding is 1, t3 is the ratio of the average thickness of the third layer when the average total thickness of the cladding is 1, and d1 is the density [g / cm 3 ], d2 is the density of the second layer [g / cm 3 ], d3 is the density of the third layer [g / cm 3 ], [Ni]1 is the mass fraction of Ni per unit mass of the first layer, [Ni]2 is the mass fraction of Ni per unit mass of the second layer, and [Ni]3 is the mass fraction of Ni per unit mass of the third layer. The middle equations of Equation 1 and Equation 2 may be written as Equation 1A and Equation 2A. (t1×d1×[Ni]1+t2×d2×[Ni]2) / (t1×d1+t2×d2) Equation 1A (t1×d1×[Ni]1+t2×d2×[Ni]2+t3×d3×[Ni]3) / (t1×d1+t2×d2+t3×d3) Equation 2A

[0051] If the value of Formula 1A or Formula 2A is less than 0.050 for the Ni mass fraction of each layer in the clad and the layer thickness ratio of each layer to the total clad thickness, the corrosion resistance of the weld metal in an alkaline environment may be reduced depending on the welding conditions when the clad is welded. Therefore, the value of Formula 1A or Formula 2A is 0.050 or greater. From the viewpoint of ensuring corrosion resistance of the weld metal in an alkaline environment, the value is preferably 0.053 or greater, more preferably 0.055 or greater, even more preferably 0.057 or greater, and most preferably 0.060 or greater. On the other hand, if the value of Formula 1A or Formula 2A exceeds 0.630, the effect of ensuring corrosion resistance of the weld metal in an alkaline environment saturates. Furthermore, the amount of nickel base metal used becomes excessively large, resulting in high costs. For these reasons, the value of Formula 1A or Formula 2A is 0.630 or less. From the viewpoint of cost reduction, it is preferably 0.625 or less, more preferably 0.620 or less, even more preferably 0.615 or less, and particularly preferably 0.613 or less. The value of Formula 1A or Formula 2A may be 0.500 or less, 0.400 or less, or 0.300 or less.

[0052] As described above, by setting the Ni mass fraction of the first layer in a two-layer clad, or the Ni mass fraction of the first and third layers in a three-layer clad, and the relationship between the layer thickness ratio of each layer within the overall clad thickness, within the appropriate ranges shown in Equations 1 and 2, the corrosion resistance of the clad weld metal in an alkaline environment can be ensured regardless of the welding conditions. The reason for this has not been determined and is merely speculation, but the following reasons are thought to be the case. As shown in Non-Patent Document 1, in a high-temperature 48% NaOH solution environment, the corrosion rate of an Fe-Ni binary alloy is suppressed below a certain level if the Ni concentration is above a certain level. Although the cause of this phenomenon is not mentioned in detail, it is thought that a similar phenomenon of corrosion suppression occurs in various alkaline solution environments at various temperatures when the metallic material exposed to the environment contains a certain amount of Ni or more. When clads are welded under various conditions depending on their intended use, the internal structure of the weld metal is expected to vary depending on the welding method and conditions, the welding material, and the components contained in the metallic material of each clad layer. However, the inventors of the present disclosure have conducted welding under various conditions and with various clad configurations and investigated the corrosion resistance of the weld metal in an alkaline environment. As a result, it has become clear that the corrosion resistance of the weld metal in an alkaline environment can be controlled by appropriately controlling variables believed to be related to the Ni concentration in the weld metal in the clad, i.e., the Ni mass fraction of each layer in the clad and the layer thickness ratio of each layer within the overall clad thickness. This is believed to be because the clad according to the present disclosure, by setting the variables believed to be related to the Ni concentration in the weld metal within a certain range, ensures that the weld metal contains at least a certain amount of Ni to fully exhibit corrosion resistance in an alkaline environment, regardless of the welding method used. This is believed to be the factor that ensures sufficient corrosion resistance of the weld metal in an alkaline environment.

[0053] 2. Method for manufacturing cladding according to the present disclosure A preferred method for manufacturing the clad according to the present disclosure will be described. The method for manufacturing the clad according to the present disclosure is not limited. An example of a method for manufacturing the clad according to the present disclosure will be described below. The following method is preferred because it allows stable manufacturing.

[0054] The clad according to the present disclosure can be manufactured through the following lamination process, roll-bonding process, cold-rolling process, and annealing process. Other processes may be included, such as a pickling process after the roll-bonding process, as needed. Note that the following mainly describes a method for manufacturing a three-layer clad, but when manufacturing a two-layer clad, the material for the third layer can be omitted.

[0055] The lamination process involves preparing the first layer material, the second layer material, and the third layer material, laminating them in that order, and temporarily joining them partially by welding the outer periphery, etc., to form a laminate. The roll-bonding step is a step in which the temporarily bonded laminate is heated to a certain temperature and hot-roll-bonded in this state to form a clad having a first layer, a second layer, and a third layer. The cold rolling step is a step in which the clad is cold rolled to a predetermined thickness to form a thin clad plate. The annealing step is a step in which the cold-rolled clad is annealed at a certain temperature in order to impart workability to the clad. Each step will be described in detail below.

[0056] (1)Lamination process In the lamination process, first, the materials for the first, second, and third layers are prepared. The shape, composition, density, thickness, etc. of each material are adjusted so that when the clad is completed, it satisfies Equation 2. In addition, in preparation for the roll-lamination process described below, it is preferable to measure the thickness of each material at multiple locations along the rolling direction and calculate the standard deviation of the thickness of each material from the measurement data. From the perspective of ease of measurement work, it is preferable that the measurement position be within a range of 10 to 50 mm from the end. Furthermore, there are 10 measurement locations, and 10 thickness measurements are taken for each material at each location. The standard deviation is calculated from the data obtained in this manner. Note that a vernier caliper is used for the measurements.

[0057] For example, hot-rolled sheets of pure nickel can be used as the material for the first and third layers, and a slab of carbon steel can be used as the material for the second layer. These materials are stacked in the thickness direction in the order of first layer, second layer, and third layer. After laminating the materials for the first, second, and third layers in this order, it is preferable to temporarily fasten the outer periphery between the first and second layers and the outer periphery between the second and third layers of the laminate by welding or the like to prevent the materials from moving (to prevent misalignment between the materials). Preferred welding methods include shielded metal arc welding, TIG welding, and MIG welding. Also, during or after welding, the gaps between the layers sealed by welding may be evacuated using a rotary pump or the like. The degree of vacuum is not specified, but from the viewpoint of bondability, a vacuum of 5.0 x 10 -1 It is preferable that the pressure is 0.01 Pa or less.

[0058] (2) Roll-bonding process The laminate obtained by the above method is subjected to hot rolling to bond the layers together to form a clad. The heating temperature before hot rolling is preferably 1000°C or higher to obtain sufficient bonding strength. From the viewpoint of bonding, it is more preferably 1050°C or higher. On the other hand, since an excessive increase in heating temperature leads to an increase in the load on the heating equipment and an increase in energy costs, it is preferably 1380°C or lower. From the viewpoint of energy costs, it is more preferably 1350°C or lower. Regarding the rolling pass schedule, roll bonding can be performed without any problems as long as the rolling reduction rate of the entire schedule is within a certain range. On the other hand, from the viewpoint of controlling the clad thickness and thickness variation, it is preferable to perform the first pass of roll bonding of the laminate under rolling conditions within a range that satisfies the following formula 3. -0.00059×T+0.812≦r1≦-0.00068×T+0.936 Formula 3 Here, T [°C] is the heating temperature of the laminate before roll bonding, and r1 is the rolling ratio of the first pass of roll bonding, which can be expressed by the following formula 4. Note that the heating temperature of the laminate in this disclosure means the temperature of the surface of the laminate when it is placed in a heating furnace and heated, and then taken out of the furnace. Here, the surface to be measured for temperature may be any surface of the laminate. r1=(cc′) / c Equation 4 Here, c (mm) is the total thickness of the laminate before roll joining, i.e., the sum of the thicknesses of the first, second, and third layer materials, and c' (mm) is the total thickness of the laminate after the first pass of roll joining. If the value of r1 falls below the lower limit (left side) of Equation 3, the thickness ratio of the laminate materials before rolling and the thickness ratio of each layer corresponding to each material in the rolled laminate (hot-rolled sheet) may change during the roll joining process, or the standard deviation of the thicknesses of the first and third cladding layers may increase. On the other hand, if the value of r1 exceeds the upper limit (right side) of Equation 3, the overall shape of the laminate after rolling may deteriorate. In addition to the above, in the roll bonding process, when producing a three-layer clad consisting of the first layer, second layer, and third layer, it is preferable to carry out the rolling under conditions that satisfy the following formulas 5 to 7 (when producing a two-layer clad consisting of the first layer and second layer, the following formulas 5 and 6). s Ni1 ×(1-r 950 )≦0.130 Equation 5 s Fe ×(1-r 950 )≦0.750 Equation 6 s Ni2 ×(1-r 950 )≦0.130 Equation 7 where s Ni1 , s Fe , s Ni2 (mm) are the standard deviations of the thicknesses of the first, second, and third layers measured during the lamination process, respectively, and r 950 is the reduction amount from the thickness in the material state to the rolling pass where the temperature after rolling falls below 950°C, and can be calculated using the following formula 8. r 950 =(cd′) / c Equation 8 Here, c (mm) is the total thickness of the laminate before roll bonding, and d' (mm) is the thickness of the laminate immediately after the rolling pass in which the post-rolling temperature first falls below 950°C during the rolling pass schedule. If the pass schedule for the roll bonding process does not satisfy the above formulas 5, 6, and 7, the standard deviations s1 and s3 of the thicknesses of the first and third layers may become large. Note that, in this disclosure, the post-rolling temperature of the laminate during rolling refers to the surface temperature of the laminate immediately after rolling in each pass. Here, the surface on which the temperature is measured may be any surface of the laminate during rolling.

[0059] (3) Cold rolling process The clad bonded by hot rolling is subjected to cold rolling to adjust the thickness to a predetermined value as a product (clad) to obtain a clad having a desired thickness. In the cold rolling pass schedule, rolling can be performed without any problems as long as the rolling reduction ratio of the entire cold rolling schedule is within a certain range. Since the hot-rolled sheet that has undergone the roll-bonding process has a large thickness when used as a material for a plant, for example, it is preferable to perform cold rolling of at least 30% or more to adjust the thickness. On the other hand, if the rolling reduction ratio is excessively increased, it will lead to an increased load on the rolling equipment, so the rolling reduction ratio is preferably 95% or less. From the viewpoint of equipment load, the rolling reduction ratio is more preferably 94% or less.

[0060] (4) Annealing process In the cold rolling process, work hardening inevitably occurs in the clad, reducing workability. Therefore, annealing is performed to obtain sufficient workability. The annealing temperature is preferably 700°C or higher, at which both the Ni-based metal layer (first and third layers) and the Fe-based alloy layer (second layer) soften. From the viewpoint of promoting softening, it is more preferably 750°C or higher. On the other hand, since an excessive temperature rise leads to an increase in the load on the annealing equipment and an increase in energy costs, the annealing temperature is preferably 1150°C or lower. From the viewpoint of energy costs, it is more preferably 1100°C or lower.

[0061] As described above, there are still many unknowns regarding the effect of managing the rolling conditions for the first pass in the roll joining process, and the effect of managing the rolling reduction ratio from the start of roll joining until the rolling pass where the temperature drops below 950°C, and this remains only speculation, but the following factors are thought to be responsible.

[0062] Regarding the range of rolling conditions for the first pass in the roll-bonding process, setting the rolling conditions within the aforementioned range during the first pass is believed to eliminate gaps between the materials not yet bonded before rolling and ensure nearly the entire bonding surface. The Fe-based alloy base material and the Ni-based clad material have different hot deformation resistances. Therefore, it is preferable to schedule the roll-bonding passes with as few passes as possible, preferably by completing the first pass, so that the base material and clad material layers are bonded over nearly the entire bonding surface. If the second and third passes proceed without bonding some of the bonding surfaces, the base material and clad material layers will be reduced at different hot deformation resistances at the unbonded bonding surfaces. Therefore, in the areas not bonded in the first pass, there is a risk that the thickness reduction rates of each layer will be different during rolling. This may result in a difference in the thickness ratio of each layer and the thickness ratio of each layer after the clad plate is produced compared to the area bonded in the first pass.

[0063] Furthermore, it is estimated that the rolling reduction ratio from the start of roll joining to the rolling pass where the post-rolling temperature falls below 950°C is such that, if almost the entire joining surface is joined in the first pass, the Fe-based alloy base material and the Ni-based metal clad material are rolled with approximately the same deformation resistance. When the Fe-based alloy base material is cooled from a high temperature range, a phase transformation from austenite to ferrite begins somewhere in the temperature range of approximately 850 to 950°C, although this depends on the composition. As a result of research by the inventors of the present disclosure, it was found that the deformation resistance of the Fe-based alloy base material changes significantly at a temperature in the range of approximately 850 to 950°C, which is thought to correspond to the temperature at which the austenite to ferrite phase transformation occurs. That is, in the temperature range between 850 and 950°C, which is considered to be the austenite phase region, the Fe-based alloy generally has the same deformation resistance as the Ni-based metal, although this depends on the type of Ni-based metal used in the cladding material. However, in the lower temperature range, where the ferrite phase is thought to begin to form, the deformation resistance significantly decreases, resulting in a difference in deformation resistance between the Fe-based alloy and the Ni-based metal. This difference in deformation resistance is thought to affect the deformation behavior at the interface between the Fe-based alloy base material and the Ni-based metal cladding material, which in turn affects the thickness variation, or standard deviation, of the cladding material. Therefore, it is thought that the rolling reduction ratio at temperatures above 950°C, where thickness variation is unlikely to occur, needs to be appropriately controlled by applying the aforementioned Equations 5 to 7 in accordance with the standard deviation of the thickness of the material before roll joining. [Example]

[0064] The effects of the present invention will be explained below using examples, but the present disclosure is not limited to the conditions used in the following examples.

[0065] [Clad manufacturing] (1) Cladding production Samples of a two-layer clad consisting of a first and second layer, and a three-layer clad consisting of a first, second, and third layer were fabricated under the following conditions. A plate of pure nickel NW2201 or Ni-based alloy NCF600 measuring 150.0 mm in width and length was prepared as the material for the first layer of each clad, or the third layer of the triple-layer clad, and carbon steel SPCE measuring 150.0 mm in width and length and having the thickness shown in Table 1 was prepared as the material for the second layer. Each material was manufactured as follows.

[0066] (Pure nickel NW2201) A hot-rolled coil of NW2201 specified in JIS G 4902:2019 was prepared, and a hot-rolled plate was cut from the hot-rolled coil, flattened, and polished with a #40 flap wheel. The plate surface was then washed with acetone and finely slashed. This exposed the metal surface on each side of the plate, and an NW2201 plate measuring 150.0 mm in width and length and having the thickness shown in Table 1 was obtained as the nickel material to be used as the cladding material (first layer and / or third layer).

[0067] (Ni-based alloy NCF600) A hot-rolled coil of NCF600 specified in JIS G 4902:2019 was prepared, and a hot-rolled sheet was cut from the hot-rolled coil, flattened, and polished with a #40 flap wheel. The sheet surface was then washed with acetone and fine-sliced. This exposed the metal surface on each side of the sheet, and an NCF600 sheet with a width and length of 150.0 mm and the thickness shown in Table 1 was obtained as the Ni-based alloy material to be used as the cladding material (first layer and / or third layer).

[0068] (Carbon steel SPCE) A slab equivalent to ordinary steel (SPCE specified in JIS G 3141:2017) was cast and hot-rolled, after which blocks were cut out from the hot-rolled material, and each face of the block was polished with a #40 flap wheel and washed with acetone. This exposed the metal surface on each face of the block, and a carbon steel SPCE with the thickness shown in Table 1 and a width and length of 150.0 mm was obtained as the carbon steel material used as the base material (second layer).

[0069] For each material, the thickness was measured in advance with a vernier caliper at 10 points, 30 mm from the end of the plate width and 10 mm apart from each other, centered on the center of the plate length. The standard deviation s Ni1 , s Fe , s Ni2 was calculated. Then, in the case of a two-layer clad, the first and second layer materials were stacked in that order, and in the case of a three-layer clad, the first, second and third layer materials were stacked in that order, and the four peripheries of the interface between each material were fixed by shielded metal arc welding to create a two-layer or three-layer laminate.

[0070] These laminates were rolled and bonded at various heating temperatures T (°C) and pass schedules to produce integrated hot-rolled sheets with a total thickness of 5.0 mm. The heating temperature before rolling, the rolling reduction ratio r1 in the first pass, and the rolling reduction ratio r2 until the laminate temperature fell below 950°C were also used. 950 The values ​​K1, K2, and L expressed by the following formulas 9 to 13 are measured. Ni1 , L Fe , L Ni2 was calculated. K1=-0.00068×T+0.936 Equation 9 K2=-0.00059×T+0.812 Equation 10 L Ni1 =s Ni1 ×(1-r 950 ) Equation 11 L Fe =s Fe ×(1-r 950 ) Equation 12 L Ni2 =s Ni2 ×(1-r 950 ) Equation 13

[0071] Thereafter, under the same conditions, cold rolling was performed at a rolling ratio of 80% and annealing was performed at 850°C, and clad samples were produced by rolling to a thickness of 1.0 mm.

[0072] Details of each clad sample prepared and the manufacturing conditions are shown in Table 1. In each table, underlines indicate that the material is outside the scope of this disclosure.

[0073] [Table 1]

[0074] For each clad sample, 10 different specimens, each 50 mm or more apart, were prepared for plate cross-section observation, with the L-shaped cross section as the observation surface. The thicknesses of the first and third layers were measured at 10 points per specimen. To calculate the standard deviation and average thickness from the thickness data for each layer at these 100 points, the L-shaped cross sections were observed, and the average thickness e (mm) and standard deviation s1 of the first layer, the average thickness f (mm) and standard deviation s2 of the second layer, and the average thickness g (mm) and standard deviation s3 of the third layer were measured. The thickness data for each layer were then used to calculate the ratio t1 of the average thickness of the first layer, t2 of the average thickness of the second layer, and t3 of the average thickness of the third layer, relative to the total clad thickness (1), and the value H defined by Equation 14 below was calculated. H=(t1×d1×[Ni]1+t2×d2×[Ni]2+t3×d3×[Ni]3) / (t1×d1+t2×d2+t3×d3) Equation 14 where d1 is the density of the first layer [g / cm 3 ], d2 is the density of the second layer [g / cm 3 ], d3 is the density of the third layer [g / cm 3 ], [Ni]1 is the mass fraction of Ni per unit mass of the first layer, [Ni]2 is the mass fraction of Ni per unit mass of the second layer, and [Ni]3 is the mass fraction of Ni per unit mass of the third layer. The NW2201, NCF600, and SPCE materials were all cut from a single block. Based on measurements of each block, the densities d1, d2, and d3 of each layer were 8.88 for NW2201, 8.40 for NCF600, and 7.85 for SPCE. The mass fraction of Ni per unit mass of each layer was 0.995 for NW2201, 0.770 for NCF600, and 0.000 for SPCE.

[0075] [evaluation] (Corrosion resistance in alkaline environments) The 1.0 mm thick clad cold-rolled sheet sample was split in half widthwise using a shear. The cross sections of the shears were then butted together and manually arc-welded along the butt line. A covered electrode, ENi2061 (JIS Z 3224:2010), was used as the welding rod. After welding, three prismatic samples measuring 1.0 mm x 1.0 mm x 30 mm were cut from the weld metal at different locations, and after measuring their mass and calculating their density, they were subjected to an immersion test in a high-temperature alkaline solution. The collected prismatic samples were degreased and washed, and their mass before the immersion test was measured. They were then immersed in a 48% NaOH aqueous solution at a water temperature of 90°C for 24 hours. The samples were then washed again, and their mass after the immersion test was measured. The corrosion rate [m / s] was calculated from the change in mass before and after the immersion test. At this time, the corrosion rate for all three prismatic samples was 3.5 x 10 -13 If the corrosion rate is less than [m / s], the corrosion resistance of the weld metal part (weld bead) is good (Y). -13 When the speed exceeded [m / s], the corrosion resistance was judged to be poor (N). Table 2 shows the details of the 1.0 mm thick clad cold-rolled sheet samples produced and the evaluation results of corrosion resistance.

[0076] [Table 2]

[0077] As shown in Table 2, the clads according to the present disclosure had good corrosion resistance of the weld metal part during welding. On the other hand, the clads outside the scope of the present disclosure had poor corrosion resistance of the weld metal part during welding. Nos. 3 and 8 did not satisfy the relationship of Equation 3 in the roll-bonding process, and when they became clad samples, they did not satisfy Equation 2. Therefore, the corrosion resistance test results of the prismatic samples did not satisfy the evaluation criteria. Nos. 4 and 7 did not satisfy the relationships of Equations 5 to 7 in the roll bonding process, and the standard deviations of the first and third layers exceeded the upper limits. As a result, the corrosion resistance test results of the prismatic samples did not satisfy the evaluation criteria. No. 13 did not satisfy the relationship of Equation 3 in the roll bonding process, and when it became a clad sample, it did not satisfy Equation 1. Therefore, the corrosion resistance test results of the prismatic sample did not satisfy the evaluation criteria. No. 14 did not satisfy the relationships of Equation 3, Equation 5, and Equation 6 in the roll bonding process, and the standard deviation of the first layer exceeded the upper limit. As a result, the corrosion resistance test results of the prismatic sample did not satisfy the evaluation criteria. From this, it was confirmed that the clad according to the present disclosure can be suitably used as a material for applications requiring corrosion resistance, particularly in alkaline environments of welded joints. [Explanation of symbols]

[0078] 1. Clad 2. First layer (cladding material) 3 2nd layer (base material) 4. Third layer (cladding material)

Claims

1. a two-layer structure including a first layer made of pure nickel or a Ni-based alloy and a second layer made of an Fe-based alloy and bonded to one surface of the first layer, or a three-layer structure further including a third layer made of pure nickel or a Ni-based alloy and bonded to the surface of the second layer opposite to the surface bonded to the first layer, The standard deviation of the thickness [μm] of the first layer is s １ , the standard deviation of the thickness [μm] of the third layer is s ３ When this is done, s １ and s ３ are each 60 μm or less, A clad that satisfies the following formula (I): 0.050 ≤ (t １ × d １ × [Ni] １ + t ２ × d ２ × [Ni] ２ + t ３ × d ３ × [Ni] ３ ) / (t １ × d １ + t ２ × d ２ + t ３ × d ３ ) ≤ 0.630 Equation (I) In the formula (I), t １ is the ratio of the average thickness of the first layer to the average total thickness of the cladding, t ２ is the ratio of the average thickness of the second layer to the average total thickness of the cladding, t ３ is the ratio of the average thickness of the third layer to the average total thickness of the cladding, d １ is the density of the first layer [g / cm ３ ], d ２ is the density of the second layer [g / cm ３ ], d ３ is the density of the third layer [g / cm ３ ], [Ni] １ is the mass ratio of Ni per unit mass of the first layer, [Ni] ２ is the mass ratio of Ni per unit mass of the second layer, [Ni] ３ is the mass ratio of Ni per unit mass of the third layer. However, in the case of the two-layer structure, in the formula (I), t ３ , d ３ , and [Ni] ３ are set to 0.

2. The cladding according to claim 1 , having the two-layer structure, wherein the average thickness of the first layer is 30 μm or more and 300 μm or less.

3. The cladding of claim 1 having a two-layer structure, wherein the first layer is pure nickel.

4. 2. The clad according to claim 1, having the three-layer structure, wherein an average thickness of at least one of the first layer and the third layer is 30 μm or more and 300 μm or less.

5. The cladding of claim 1 having a three-layer structure, wherein at least one of the first layer and the third layer is pure nickel.

6. The clad according to any one of claims 1 to 5, wherein the average total thickness is greater than 0.1 mm and not greater than 3.0 mm.

Images