Clad

Abstract

A clad 1 includes a first layer 2 and a third layer 4 made of pure nickel or an Ni-based alloy, and a second layer 3 made of an Fe-based alloy. Standard deviations s1 and s3 of the thicknesses [μm] of the first layer and the third layer are each 60 [μm] or less, and the clad satisfies the following expression.　0.050≤(t1×d1×[Ni]1+t2×d2×[Ni]2+t3×d3×[Ni]3) / (t1×d1+t2×d2+t3×d3)≤0.630. In the expression, t1, t2, and t3 are the respective proportions of the thicknesses of the first layer, the second layer, and the third layer when the total thickness of the clad is taken as 1, d1, d2, and d3 are the respective densities [g / cm3] of the first layer, the second layer, and the third layer, and [Ni]1, [Ni]2, and [Ni]3 are the respective mass fractions of Ni per unit mass of the first layer, the second layer, and the third layer. The clad may be composed of the first layer and the second layer.

Description

Clad

[0001] This disclosure relates to cladding.

[0002] Nickel sheets and Ni-based alloy sheets are used in chemical plants that handle alkaline solutions, as well as in electrode materials for secondary batteries used in electrification technologies for various industrial products such as electric vehicles, and in hydrogen storage alloys used for hydrogen transport. In particular, these products are indispensable for realizing a carbon-neutral society to mitigate climate change caused by greenhouse gases such as carbon dioxide, and the demand for nickel ingots used in these products is expected to increase further in the future. In addition, because nickel ingot prices tend to fluctuate sharply due to changes in the global supply and demand balance of nickel ore, there is a need for materials that can reduce the amount of nickel ingot used while making use of the properties of nickel.

[0003] Pure nickel (Ni) and certain Ni-based alloys (in this disclosure, pure nickel and Ni-based alloys may be collectively referred to as "Ni-based metals") exhibit 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 may be possible to reduce material costs by using a general-purpose and inexpensive metal material for the inner layer and a plate material with a certain thickness or more of Ni-based metal for the outer layer.

[0004] 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. 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, and the exposure rate of iron at the outermost surface of the nickel plating layer is 30% or less. Such 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 by applying heat treatment after plating as necessary. Since the thickness of the plating layer of such a multi-layered material is thin compared to the thickness of the base steel sheet, the amount of Ni used can be reduced. However, because the plating layer is thin, for example, if bending is required when used as a plant component, the plating layer may break at the outer circumference of the bend, exposing the Fe of the carbon steel, which may locally reduce corrosion resistance. On the other hand, increasing the thickness of the plating layer is generally difficult and inefficient.

[0005] Another example of a multilayer material is a clad material (sometimes simply referred to as "clad") in which a cladding material that imparts new functionality is joined 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 by hot rolling an assembled material in which a set of a base material made of carbon steel and a cladding material made of one of the following: stainless steel, pure nickel, and Ni-based alloy, is overlapped and the peripheral edges are welded.

[0006] Patent document 1: Japanese Patent Application Publication No. 6-2104 Patent document 2: Japanese Patent Application Publication No. 1992-192404

[0007] Non-patent document 1: Takashi Sakaki, Yoki Shimizu, Tosoh Research Report, Vol. 33, No. 1, (1989), pp. 45-55.

[0008] Nickel-clad steels specified in Patent Document 2 and JIS G 3602:2012 are thick, and in particular, those specified in JIS only specify the thickness of the outer nickel layer of the cladding material as 1 mm or more, less than 5 mm, or 5 mm or more. With regard to cladding, the manufacturing and usage challenges common to both thick and thin plate materials, as well as the manufacturing and usage challenges specific to thin plate materials, have not been considered until now.

[0009] In industrial product components exposed to alkaline environments, nickel plates are expected to undergo not only bending but also welding and other processing. When using clad plates, for example, with nickel as the base material and carbon steel as the core material, as a substitute for nickel plates, depending on the welding conditions, the internal carbon steel core material may be exposed, potentially leading to a localized decrease in alkali corrosion resistance. Furthermore, in the welding process of clad plates, Fe may be locally exposed in the weld metal portion (in this disclosure, "weld metal portion" means "weld bead"), potentially reducing alkali corrosion resistance. In particular, there are cases where almost the entire weld metal portion has low corrosion resistance, and cases where areas with high and low corrosion resistance are mixed within the weld metal portion.

[0010] This disclosure was made in view of the above-mentioned problems. Specifically, the purpose of this disclosure is to provide a cladding material that keeps material costs low and ensures corrosion resistance of the welded metal in an alkaline environment even after welding.

[0011] The above problem is solved by the following means: <1> A two-layer structure comprising 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 side of the first layer, or a three-layer structure further comprising a third layer made of pure nickel or a Ni-based alloy bonded to the side of the second layer opposite to the side bonded to the first layer, wherein 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 that happens, s １ and s ３ A cladding in which each of the following equations (I) is 60 [μm] or less and satisfies the following formula: 0.050 ≤ (t １ ×d１ ×[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 Formula (I) In the aforementioned formula (I), t １ is the ratio of the average thickness of the first layer when the average total thickness of the cladding is taken as 1, t ２ is the ratio of the average thickness of the second layer when the average total thickness of the cladding is taken as 1, t ３ is the ratio of the average thickness of the third layer when the average total thickness of the cladding is taken as 1, 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 proportion of Ni per unit mass of the first layer, [Ni] ２ is the mass proportion of Ni per unit mass of the second layer, [Ni] ３ is the mass proportion of Ni per unit mass of the third layer. However, in the case of the aforementioned two-layer structure, in the aforementioned formula (I), t ３ , d ３ , and [Ni] ３Each of these values ​​shall be 0. <2> The cladding according to <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 according to <1> or <2>, having the two-layer structure, wherein the first layer is pure nickel. <4> The cladding according to <1>, having the three-layer structure, wherein 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. <5> The cladding according to <1> or <4>, having the three-layer structure, wherein at least one of the first layer and the third layer is pure nickel. <6> The cladding according to any one of <1> to <5>, wherein the average of the total thickness is greater than 0.1 mm and 3.0 mm or less.

[0012] According to this disclosure, a cladding material is provided that keeps material costs low and ensures corrosion resistance of the welded metal in an alkaline environment even after welding.

[0013] This is a schematic diagram showing the overall structure of a cladding having a three-layer structure, which is an example of the cladding related to this disclosure.

[0014] An embodiment, which is an example of this disclosure, will be described. In this disclosure, a numerical range expressed using "~" means a range that includes the numbers written before and after "~" as the lower and upper limits. However, if the numbers written 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. The elemental content of the chemical composition may be expressed by adding "amount" to the element symbol (for example, C amount, Si amount, etc.). Regarding the elemental content of the chemical composition, "%" means "mass %". When "0~" is written regarding the elemental content of the chemical composition, it means that the element does not need to be included. The term "process" is included not only in the case of an independent process, but also in the case of a process that cannot be clearly distinguished from other processes, as long as the intended purpose of that process is achieved.

[0015] The present inventors have diligently studied to solve the above problems and have obtained the following findings: (A) When a cladding material, which is an Fe-based alloy such as carbon steel as the base material and a Ni-based metal as the cladding material, is joined to other members by welding, there is a possibility that Fe may be exposed in the molten metal portion due to the partial melting of the base material layer of the cladding material. (B) In the weld metal portion of a thin plate of cladding material, which is an Fe-based alloy such as carbon steel as the base material and a Ni-based metal as the cladding material, the components of the Fe-based alloy and the Ni-based metal are mixed by melting, and although the formation of intermetallic compounds is possible, it is expected that the weld metal portion will basically be an alloy mainly composed of Ni and Fe. (C) As shown in Non-Patent Literature 1, in an alkaline environment, it is expected that the corrosion resistance of an alloy mainly composed of Ni and Fe will be improved by containing a certain amount of Ni or more, and sufficient corrosion resistance can be ensured. From this, it is necessary that the Ni concentration of the weld metal portion be above a certain level in order to ensure the corrosion resistance of the weld metal portion. (D) Welding conditions vary depending on the application, product, or welder, and there is a possibility of large variations in the state of the weld metal, especially its Ni concentration. For this reason, the amount of Ni contained in the weld metal must remain as stable as possible and above a certain level, regardless of the welding conditions under which the cladding is welded. (E) Regarding the Ni concentration in the weld metal, in the case of welding using welding materials such as welding rods and welding wires, although there is an influence from the components contained in the welding materials, it is thought that the majority of the variation is due to the Ni concentration of the cladding layer made of Ni-based metal and the value of the thickness of the cladding layer relative to the total thickness. For this reason, by making the cladding such that the Ni concentration of the cladding layer made of Ni-based metal and the value of the thickness of the cladding layer relative to the total thickness are within a certain range, the amount of Ni contained in the weld metal can be kept above a certain level regardless of the welding method. (F) Depending on the manufacturing method, the thickness of the cladding layer of the cladding may vary greatly from place to place on the plate. In places where the thickness of the cladding layer is thin, the Ni concentration derived from the cladding material contained in the weld metal may drop excessively. On the other hand, in cladding where the thickness of the bonding layer is locally increased, it ends up requiring more nickel ingot than necessary, making it difficult to achieve cost reduction.Therefore, it is preferable that the deviation in the thickness of the laminated material layer within the clad sheet is within a certain range.

[0016] The cladding described herein was created based on the above findings. Specifically, the cladding described herein 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 side 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 side of the second layer opposite to the side 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 of the third layer [μm] is s ３ When that happens, s １ and s ３ Each of these is 60 [μm] or less, and satisfies the following equation (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 Equation (I), t １ t is the ratio of the average thickness of the first layer when the average total thickness of the cladding is set to 1. ２ t is the ratio of the average thickness of the second layer when the average total thickness of the cladding is set to 1. ３ d is the ratio of the average thickness of the third layer when the average total thickness of the cladding is set to 1. １ The density of the first layer [g / cm³] ３ ), d ２ The density of the second layer [g / cm³] ３ ), d ３ The density of the third layer [g / cm³] ３ ] [Ni] １ This is the mass ratio of Ni per unit mass of the first layer, [Ni] ２This is the mass percentage 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 a two-layer structure, in formula (I) above, t ３ d ３ , and [Ni] ３ These values ​​are set to 0. In the following explanation, "main component" means the element that makes up the largest amount (mass%) of the elements constituting the metal material, preferably 50% or more.

[0017] 1. Cladding relating to this disclosure (1) Overall structure The cladding relating to this disclosure has a two-layer structure or a three-layer structure. Figure 1 is a schematic diagram showing the overall structure of a cladding having a three-layer structure, which is an example of the cladding relating to this disclosure (in this disclosure, a cladding having a two-layer structure may be referred to as a "two-layer cladding," and a cladding having a three-layer structure may be referred to as a "three-layer cladding"). As shown in Figure 1, the three-layer cladding 1 comprises a first layer 2, a second layer 3, and a third layer 4 which is provided as needed. The first layer 2 is joined to one of the two sides of the second layer 3, and the third layer 4 is joined to the other side (i.e., the side of the second layer 3 opposite to the side joined to the first layer 2). The following explanation will mainly use the three-layer cladding as an example. In the case of two-layer cladding, it consists of the first layer 2 and the second layer 3, and is the same as three-layer cladding 1 except that there is no third layer 4.

[0018] (2) The first and third layers The first layer 2 and the third layer 4 are made of a Ni-based metal with Ni as the main component. There is no specific requirement for the type of Ni-based metal, but typical examples include various Ni-based alloys as described in JIS G 4902:2019, and pure nickel. From the viewpoint of corrosion resistance, the use of pure nickel is preferred.

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

[0020] The standard deviation of the thickness of the first layer of the cladding relating to this disclosure is s １ The standard deviation of the thickness of the third layer is s ３ When that happens, s １ and s ３Each of these is 60 μm or less. The cladding is joined via the weld metal during welding. The weld metal is thought to contain Ni mainly derived from the Ni-based metal of the first and third layers, which serve as the cladding material. The corrosion resistance of the weld metal in an alkaline environment is thought to be influenced by the amount of Ni contained in the weld metal. The cladding according to this disclosure can ensure sufficient corrosion resistance of the weld metal in an alkaline environment after welding by setting the thickness configuration of each layer within an appropriate range, as described later. The distribution of the thickness of the first layer and the thickness distribution of the third layer, i.e., the standard deviation, is important when setting this thickness configuration. Due to the manufacturing process, multilayer materials such as cladding inevitably have variations in the thickness of each layer from place to place, i.e., variations. The thickness configuration of each layer constituting the cladding from place to place affects the variation in the corrosion resistance of the weld metal formed when welding is performed at that location in an alkaline environment, so it is preferable to keep the variation in the cladding from place to place as small as possible. Therefore, the standard deviations of the thicknesses of the first and third layers of the cladding according to this disclosure are 60 μm or less, respectively. From the viewpoint of ensuring corrosion resistance of the weld metal in an alkaline environment throughout the cladding, the standard deviation 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 root mean square of the difference between the measured thickness values ​​of each layer and the average value, and is expressed by the following formula (II).

[0021]

[0022] However, s is the standard deviation, n is the number of measurement points for the layer thickness, and x ｉ This is the value of the layer thickness measured at the i-th measurement point out of all n measurement points for the layer thickness, x ａｖｅ This is the average value of the layer thickness at all n measurement points.

[0023] The average thickness of the first layer and the average thickness of the third layer of the cladding 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 or Ni-based alloy, are made too thin, when subjected to severe bending, the layers on the outer periphery of the bend may break, exposing the Fe-based alloy that forms the base material, which may reduce corrosion resistance. In addition, when welding is performed, the corrosion resistance of the weld metal may be reduced. For this reason, the average thickness of the first and third layers is preferably 30 μm or more, respectively. 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 and third layers are made excessively thick, the material costs will increase unnecessarily. Therefore, it is preferable that the average thickness of the first and third layers be 300 μm or less. From a cost standpoint, the average thickness of the first and third layers is more preferably 275 μm or less, and even more preferably 250 μm or less. The average thicknesses of the first and third layers may be the same, and it is also acceptable to have different average thicknesses depending on the application. The method for measuring the standard deviation and average thickness of each layer is as follows: For 10 different locations on the cladding, separated by at least 50 mm from each other, a plate cross-section observation sample is prepared with the observation surface being a plane (L-section) parallel to the rolling direction and the thickness direction. Within the 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 for each layer thickness at 100 points. The cross-section of the cladding is surface polished and measured using an optical microscope at an observation magnification of 50x. Although the iron-based alloy and Ni-based alloy can be distinguished without etching, if they are difficult to distinguish, the cross-section may be surface-polished and then etched with Nital to measure the thickness of each layer.

[0025] (3) Second layer The second layer consists of an Fe-based alloy with Fe as the main component. The Fe-based alloy preferably has an Fe content of 50%, but may be 60% or more, 70% or more, 80% by mass or more, or 90% by mass or more. There is no particular requirement for the type of Fe-based alloy, but examples include carbon steel, stainless steel, nickel steel, nickel-chromium steel, nickel-chromium-molybdenum steel, chromium steel, chromium-molybdenum steel, manganese steel, etc. From the viewpoint of cost, the use of carbon steel is preferred. As for the type of carbon steel, for example, SPCC, SPCD, SPCE, SPCF, and SPCG as specified in JIS G 3141:2021 can be used.

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

[0027] C: 1.0% or less. C, by solid-solubilizing as an interstitial element in Fe-based alloys, improves the strength of Fe-based alloys as a solid-solution strengthening element. In addition, it contributes to precipitation strengthening by forming carbides with Fe, Cr, Ti, Nb, etc. For this reason, the appropriate addition of C contributes to improving the strength of the cladding. On the other hand, excessive addition of C may lead to a decrease in the ductility and workability of the cladding, so the C 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 less than 0.1%. Even with a low C content, the cladding effect according to this disclosure is fully exhibited, so there is no particular lower limit. However, if the C content is reduced to less than 0.001%, the manufacturing cost associated with removing C increases significantly. For this reason, the C content is preferably 0.001% or more. From the viewpoint of manufacturing cost, it is more preferably 0.002% or more, and 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, depending on the application, Si can be added to Fe-based alloys when these effects are required. On the other hand, excessive addition of Si may lead to a decrease in the ductility and workability of the cladding. For this reason, 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%. Even at low Si content, the cladding effect according to this disclosure is fully exhibited, so there is no particular lower limit. However, since Si is a useful element in the deoxidation process of Fe-based alloys, it is preferable that the Si content be 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. It is also a solid solution strengthening element, thus improving the strength of Fe-based alloys. Furthermore, since Mn can be introduced from raw material scrap, excessively suppressing the Mn content would necessitate reducing the use of scrap as a raw material during the refining of Fe-based alloys. This is undesirable from the standpoint of resource recycling of metal resources. From these perspectives, a certain amount of Mn content is acceptable. On the other hand, excessive addition of Mn may lead to a decrease in the ductility and workability of the cladding. Therefore, it is preferable that the Mn content be 3.0% or less. From the viewpoint of workability, it is more preferable to be 1.5% or less, even more preferably less than 1.0%, and most preferably less than 0.5%. Even at low Mn content levels, the cladding exhibits sufficient effects according to this disclosure, so there is no particular lower limit. However, if the Mn content is made excessively low, the flexibility of utilizing the scrap decreases, so it is preferably 0.001% or more. From the viewpoint of utilizing the scrap, it 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 the raw material for Fe-based alloys. Since 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, there is no particular lower limit. However, it is difficult to remove P during the refining of Fe-based alloys, and in order to reduce the P content, it is necessary to use ferrochrome with a low P concentration as a raw material. Since ferrochrome with a low P concentration is expensive, costs will increase if the P content is reduced more than necessary. For this reason, 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, etc. 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, there is no particular lower limit. However, if the S content is reduced more than necessary, the desulfurization load during the refining of the Fe-based alloy increases, and the manufacturing cost increases. For this reason, the S content is preferably 0.00001% or more, 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. Al, like Si and Mn, is an effective deoxidizing element during the refining of Fe-based alloys. On the other hand, if the Al content is too high, it may cause a decrease in 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. Even at low Al content, the cladding effect according to this disclosure is fully exhibited, so there is no particular lower limit. However, Al is one of the important deoxidizing elements, and if it is not used, the degree of freedom in the deoxidation process of Fe-based alloys may be lost. For this reason, the Al content is preferably 0.001% or more. From the viewpoint of deoxidizing 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, if the Fe-based alloy contains C, N, etc., some of the Ti reacts with C and N to form carbides or nitrides, thereby contributing to precipitation strengthening. On the other hand, if the Ti content is excessive, the hot workability and cold workability may be significantly reduced. 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. Even with a low Ti content, the cladding effect according to this disclosure is fully exhibited, so there is no particular lower limit. However, depending on the application of the cladding, strength is required, and when 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 to significant grain boundary segregation of B, which may conversely reduce hot workability. For this reason, the content of B 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. Even at low content levels, B fully exhibits the effects of a cladding according to this disclosure, so there is no particular lower limit. However, since adding an appropriate amount improves hot workability during manufacturing, an addition of 0.0001% or more is preferred. More preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0035] N: 0.05% or less. Like C, N acts as an interstitial element in Fe-based alloys, forming solid solutions to improve the strength of Fe-based alloys as a solid solution strengthening element. It also forms nitrides with Fe, Cr, Ti, Nb, etc., contributing to precipitation strengthening. Therefore, an appropriate amount of N contributes to improving the strength of the cladding. On the other hand, excessive addition of N may lead to a decrease in the ductility and workability of the cladding. For this reason, 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. Even at low N content, the cladding exhibits sufficient effects according to this disclosure, so there is no particular lower limit. However, if strength is required depending on the application of the cladding and 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 improves their strength through solid solution. However, excessive addition 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. Even at low Mo content levels, the cladding effect according to this disclosure is fully realized, so there is no particular lower limit. However, depending on the application of the cladding, strength is required, 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 simultaneously improves strength through solid solution. However, excessive addition may increase the cost of the alloy and reduce ductility and workability. For this reason, the Cr content is preferably 2.0% or less. From the viewpoint 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. Even with a low Cr content, the cladding effect according to this disclosure is fully exhibited, so there is no particular lower limit. However, depending on the application of the cladding, strength is required, and when 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 through solid solution. However, excessive addition may increase the cost of the alloy and reduce ductility and workability. For this reason, the Ni content is preferably 3.0% or less. From the viewpoint of workability and cost, it is more preferably 2.0% or less, and even more preferably 1.0% or less. Even with a low Ni content, the cladding effect according to this disclosure is fully exhibited, so there is no particular lower limit. However, depending on the application of the cladding, strength, or corrosion resistance and delayed fracture resistance of the Fe-based alloy may be required, and when Ni is utilized, 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 of Fe-based alloys, especially high-temperature strength, 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. Even with a low Cu content, the cladding effect according to this disclosure is fully exhibited, so there is no particular lower limit. However, if strength is required depending on the application of the cladding and 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, if the Fe-based alloy contains C, N, etc., some of it reacts with C and N to form carbides or nitrides, thus contributing to precipitation strengthening. On the other hand, if the Nb content is excessive, there is a risk that the hot workability and cold workability will be significantly reduced. For this reason, the Nb 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. Even with a low Nb content, the cladding effect according to this disclosure is fully exhibited, so there is no particular lower limit. However, depending on the application of the cladding, strength is required, and when Nb is utilized, it is preferable that the Nb content is 0.0005% or more. From the viewpoint of ensuring strength, it is more preferably 0.001% or more.

[0041] V: 0.7% or less V contributes to solid solution strengthening of Fe-based alloys. Furthermore, if the Fe-based alloy contains C, N, etc., some of V reacts with C and N to form carbides or nitrides, thereby contributing to precipitation strengthening. On the other hand, if the V content is excessive, the hot workability and cold workability may be significantly reduced. 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. Even at low V content, the cladding effect according to this disclosure is fully exhibited, so there is no particular lower limit. However, depending on the application of the cladding, strength is required, 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, improving hot workability and enhancing manufacturability. On the other hand, 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. Even at low Ca content, the cladding effect according to this disclosure is fully exhibited, so there is no particular lower limit. However, when Ca is used to obtain the desulfurizing effect during refining, the Ca content is preferably 0.00005% or more. From the viewpoint of desulfurizing effect, it is more preferably 0.00007% or more, and 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 enhancing manufacturability. On the other hand, excessive Mg content impairs hot workability. For this reason, the Mg 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. Even at low Mg content, the cladding effect described herein is fully exhibited, so there is no particular lower limit. However, when Mg is used to obtain the desulfurizing effect during refining, the Mg content is preferably 0.00005% or more. From the viewpoint of desulfurizing effect, it is more preferably 0.00007% or more, and even more preferably 0.0001% or more.

[0044] O: 0.01% or less. O is an element that can inevitably be present, and it can impair the processability of the cladding by forming oxides. Therefore, it is preferable that the O content be 0.01% or less. From the viewpoint of ensuring processability, it is more preferable to be 0.007% or less, and even more preferable to be 0.005% or less. Since a lower O content is preferable, there is no particular lower limit. However, if the O content is reduced more than necessary, the deoxidation process during the refining of the Fe-based alloy will be more difficult, and the manufacturing cost will increase. Therefore, it is preferable that the O content be 0.00001% or more. From the viewpoint of manufacturing cost, it is more preferable to be 0.00002% or more, even more preferable to be 0.00005% or more, and most preferably to be 0.0001% or more.

[0045] Ta: 0.5% or less. Ta contributes to solid solution strengthening of Fe-based alloys. Furthermore, if the Fe-based alloy contains C, N, etc., some of it reacts with C and N to form carbides or nitrides, thus contributing to precipitation strengthening. On the other hand, if the Ta content is excessive, the hot workability and cold workability may be significantly reduced. 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. Even with a low Ta content, the cladding effect according to this disclosure is fully exhibited, so there is no particular lower limit. However, depending on the application of the cladding, strength is required, and when 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 enhances the corrosion resistance of Fe-based alloys and improves strength through solid solution. However, excessive addition 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. Even at low W content, the cladding effect described herein is fully exhibited, so there is no particular lower limit. However, if strength is required depending on the application of the cladding and 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) improves the hot workability of Fe-based alloys. It also improves the corrosion resistance of Fe-based alloys. On the other hand, if the REM content is excessive, the hot workability may decrease. 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 REM fully exhibits its cladding effect as described in this disclosure even at low content levels, there is no particular lower limit. However, when REM is used 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 above REM content means the total content of these elements. Industrially, REM is often added in the form of mischmetal.

[0048] Remainder: Fe and impurities. The remainder of the above consists of Fe and impurities. Examples of impurities include those contained in the raw materials of Fe-based alloys, such as ore and scrap, and those introduced during the manufacturing process. Examples include Zn, Sn, Hf, Zr, Co, etc.

[0049] (4) Total Thickness of Cladding The average total thickness of the cladding according to the present disclosure is preferably more than 0.1 mm and 3.0 mm or less. When the cladding according to the present disclosure is used as a replacement for pure nickel thin plates that have conventionally been used in applications such as plants and batteries, it is required to have equivalent corrosion resistance, mechanical properties and workability. In addition, conventionally manufactured thick clad plates may pose a risk of dimensional problems when used as a replacement for pure nickel thin plates. For this reason, the average total thickness of the cladding is preferably 3.0 mm or less. From the viewpoint of ensuring workability, particularly bendability, it is more preferably 2.75 mm or less, and still more preferably 2.5 mm or less. On the other hand, if the thickness is too small, it may be difficult to maintain the structure in some applications. For this reason, the average total thickness of the cladding is preferably more than 0.1 mm. From the viewpoint of maintaining the structure as a mechanical member, it is more preferably 0.15 mm or more, still more preferably 0.2 mm or more, and most preferably 0.25 mm or more. The method for measuring the average total thickness of the cladding is to perform measurement with a micrometer at 10 different positions in the product that are 50 mm or more apart from each other, and determine the average value of the measured values.

[0050] (5) Relationship between Ni mass ratios in the first layer and the third layer, and the total thickness ratio of each cladding layer In the case where the cladding according to the present disclosure is a two-layer cladding composed of the aforementioned first layer and second layer, the following formula 1 is satisfied. 0.050≦(t １ ×d １ ×[Ni] １ +t ２ ×d ２ ×[Ni] ２ ) / (t １ ×d １ +t ２ ×d ２ )≦0.630 Formula 1 Further, in the case of a three-layer cladding composed of the aforementioned first layer and second layer plus a third layer, the following formula 2 is satisfied. 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 2 where, t １ is the ratio of the average thickness of the first layer when the average total thickness of the cladding is taken as 1, t ２ is the ratio of the average thickness of the second layer when the average total thickness of the cladding is taken as 1, t ３ is the ratio of the average thickness of the third layer when the average total thickness of the cladding is taken as 1, 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 proportion of Ni per unit mass of the first layer, [Ni] ２ is the mass proportion of Ni per unit mass of the second layer, [Ni] ３ is the mass proportion of Ni per unit mass of the third layer. The expressions in the middle of Equation 1 and Equation 2 may be referred to as Equation 1A and Equation 2A, respectively. (t １ ×d １ ×[Ni] １ +t ２ ×d ２ ×[Ni] ２ ) / (t １ ×d １ +t ２ ×d ２ ) Equation 1A (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 ) Equation 2A

[0051] If the Ni mass ratio of each layer in the cladding, and the layer thickness ratio of each layer to the total thickness of the cladding, are configured such that the value of formula 1A or formula 2A is less than 0.050, then when the cladding is welded, depending on the welding conditions, the corrosion resistance of the weld metal in an alkaline environment may decrease. For this reason, the value of formula 1A or formula 2A is 0.050 or higher. From the viewpoint of ensuring corrosion resistance of the weld metal in an alkaline environment, it is preferably 0.053 or higher, more preferably 0.055 or higher, even more preferably 0.057 or higher, and most preferably 0.060 or higher. 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. Also, the amount of nickel ingot used becomes excessively large, increasing costs. For these reasons, the value of formula 1A or formula 2A is 0.630 or lower. From the viewpoint of cost reduction, the value 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. In addition, 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 relationship between the Ni mass ratio of the first layer in a two-layer cladding, or the Ni mass ratio of the first and third layers in a three-layer cladding, and the layer thickness ratio of each layer within the total cladding thickness, to the appropriate range shown in Equations 1 and 2, the corrosion resistance of the weld metal portion of the cladding in an alkaline environment is ensured regardless of welding conditions. The reasons for this have not been definitively determined and remain speculative, but the following reasons are possible. As shown in Non-Patent Literature 1, in a high-temperature 48% NaOH solution environment, the corrosion rate of Fe-Ni binary alloys is suppressed to below a certain level when the Ni concentration is above a certain level. Although the details of the factors for this phenomenon are not mentioned, it is thought that, similarly, in environments with various alkaline solutions at various temperatures, if the metal material exposed to that environment contains a certain amount or more of Ni, a similar phenomenon of suppressed corrosion occurs. When cladding is welded under various conditions depending on the application, the internal structure of the weld metal portion is expected to change in various ways depending on the welding method and conditions, the welding material, and the components contained in the metal material of each layer of the cladding. However, the inventors of this disclosure have investigated the corrosion resistance of the weld metal in an alkaline environment by performing welding under various conditions and cladding configurations. As a result, it has become clear that the corrosion resistance of the weld metal in an alkaline environment can be controlled to a certain extent by appropriately controlling variables that seem to be related to the concentration of Ni in the weld metal within the cladding, namely the Ni mass ratio of each layer in the cladding and the layer thickness ratio of each layer within the total thickness of the cladding. This is thought to be because the cladding according to this disclosure sets the variables that seem to be related to the Ni concentration in the weld metal within a certain range, so that regardless of the welding method used, the weld metal contains a certain amount of Ni or more necessary to exhibit sufficient corrosion resistance in an alkaline environment. This is considered to be the factor that ensures sufficient corrosion resistance of the weld metal in an alkaline environment.

[0053] 2. Method for Manufacturing the Clad According to the Disclosure A preferred method for manufacturing the clad according to the disclosure is described below. The method for manufacturing the clad according to the disclosure is not limited. An example of a method for manufacturing the clad according to the disclosure is described below. The following method is preferred because it allows for stable production.

[0054] The cladding material according to this disclosure can be manufactured through the following lamination, rolling, joining, cold rolling, and annealing processes. Other processes may also be included, for example, a pickling process may be added after the rolling and joining process as needed. The following explanation will mainly use a method for manufacturing a three-layer cladding material as an example, but when manufacturing a two-layer cladding material, the third layer material may be omitted.

[0055] The lamination process involves preparing the materials for the first, second, and third layers, laminating them in that order, and partially joining them by welding or other means on the outer periphery to form a laminate. The rolling joining process involves heating the temporarily joined laminate to a certain temperature and then rolling it while still hot to form a cladding having the first, second, and third layers. The cold rolling process involves rolling the cladding to a predetermined thickness while cold to form a thin sheet of cladding. The annealing process involves annealing the cold-rolled cladding at a certain temperature to impart workability to it. Each process will be explained 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 the completed cladding satisfies Equation 2. In addition, in preparation for the rolling lamination process described later, 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 viewpoint of ease of measurement, it is preferable to measure within a range of 10 to 50 mm from the edge. In addition, there are 10 measurement locations, and at each location, 10 measurement points are taken for the thickness of each material. The standard deviation is calculated from the data obtained in this way. A caliper is used for measurement.

[0057] For example, hot-rolled pure nickel sheets can be used as the material for the first and third layers, and a carbon steel slab can be used as the material for the second layer. These materials are laminated in the thickness direction in the order of the first, second, and third layers. 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 between the second and third layers of the laminate by welding or the like to prevent the materials from moving (shifting between materials). 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 gaps between each layer sealed by welding using a rotary pump or the like. There is no specific requirement for the degree of vacuum, but from the viewpoint of jointability, 5.0 × 10 －１ It is preferable that the pressure be Pa or less.

[0058] (2) Rolling and joining process The laminate obtained by the above method is subjected to hot rolling to join the layers together to form a cladding. The heating temperature before hot rolling is preferably 1000°C or higher in order to obtain sufficient joining strength. From the viewpoint of joinability, it is more preferably 1050°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 preferably 1380°C or lower. From the viewpoint of energy cost, it is more preferably 1350°C or lower. Regarding the rolling pass schedule, rolling and joining can be performed without problems as long as the rolling rate of the entire schedule is within a certain range. On the other hand, from the viewpoint of controlling the thickness of the cladding and variations in thickness, it is preferable to carry out the first pass of rolling and joining the laminate under rolling conditions within the range that satisfies the following equation 3: -0.00059 × T + 0.812 ≤ r １ ≤ -0.00068 × T + 0.936 Equation 3 Here, T [°C] is the heating temperature of the laminate before rolling and joining, r １ is the rolling ratio of the first pass of the rolling joint, and can be expressed by the following formula 4. Note that the heating temperature of the laminate in this disclosure refers to the surface temperature of the laminate at the time it is removed from the heating furnace after being heated in the furnace. Here, any surface of the laminate can be used to measure the temperature. r １= (c - c') / c Equation 4 Here, c (mm) is the total 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 c' (mm) is the total thickness of the laminate after rolling in the first pass of rolling and joining. r １ If the value of falls below the lower limit (left side) of Equation 3, in the rolling bonding process, the thickness ratio of the materials in the laminate before rolling and the thickness ratio of each layer corresponding to each material in the laminate after rolling (hot-rolled sheet) may change, or the standard deviation of the thickness of the first and third layers, which are bonding layers, may increase. On the other hand, r １ If the value of exceeds the upper limit (right side) of Equation 3 during rolling, the overall shape of the laminate after rolling may deteriorate. In addition to the above, in the rolling and joining process, when manufacturing a three-layer cladding consisting of the first, second, and third layers, it is preferable to carry out the process under rolling conditions within the range that satisfy the following Equations 5 to 7 (when manufacturing a two-layer cladding consisting of the first and second layers, Equations 5 and 6 below). 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 Here, s Ｎｉ１ s Ｆｅ s Ｎｉ２ (mm) represents the standard deviation of the thickness of the first, second, and third layers measured during the lamination process, and r ９５０ This is the amount of reduction from the thickness of the raw material to the rolling pass where the temperature after rolling falls below 950°C, and can be calculated using the following formula 8. ９５０ = (c - d') / c Equation 8 Here, c (mm) is the total thickness of the laminate before rolling and joining, and d' (mm) is the thickness of the laminate immediately after the rolling pass in the rolling pass schedule in which the post-rolling temperature first falls below 950°C. If the rolling and joining pass schedule does not satisfy the above equations 5, 6, and 7, the standard deviation s of the thickness of each layer, the first and third layers. １ s ３There is a risk that the size may become too large. 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 cladding joined by hot rolling is cold-rolled to adjust the thickness to a predetermined value for the product (cladding) to obtain cladding of the desired thickness. In the cold rolling pass schedule, rolling can be performed without problems as long as the rolling rate of the entire cold rolling schedule is within a certain range. Hot-rolled sheets that have gone through the rolling joining process are thick when used as materials for plants, for example, 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 the rolling rate at 94% or less.

[0060] (4) Annealing Process In the cold rolling process, work hardening inevitably occurs in the cladding, 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 Ni-based metal layers (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, 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.

[0061] Regarding the effects of controlling the rolling conditions in the first pass of the rolling and joining process, as well as the effects of controlling the rolling rate from the start of rolling and joining until the rolling pass below 950°C, many aspects remain unclear and are still speculative, but the following factors are possible.

[0062] Regarding the specification of the rolling conditions range for the first pass in the rolling joining process, it is considered that setting the rolling conditions within the aforementioned range in the first pass eliminates the gaps between the materials that were not joined before rolling, resulting in a situation where almost the entire joining surface is joined. The base material, which is an Fe-based alloy, and the cladding material, which is a Ni-based metal, have different hot deformation resistances. Therefore, in the rolling joining pass schedule, it is preferable that the base material layer and the cladding material layer be joined to almost the entire joining surface by the completion of the first pass, preferably with as few passes as possible. If the reduction continues through the second and third passes without joining some of the joining surfaces being joined, the base material layer and the cladding material layer will be reduced with different hot deformation resistances in those unjoined areas of the joining surface. Therefore, in areas not joined in the first pass, there is a risk that the thinning rate during rolling of each layer will differ, and the ratio of the thickness of each layer after it has been manufactured as a clad plate may differ from that of the areas joined in the first pass.

[0063] Furthermore, the rolling rate from the start of rolling and joining to the rolling pass where the post-rolling temperature falls below 950°C is estimated to be 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 composite material are rolled with approximately the same deformation resistance. Depending on the composition, the Fe-based alloy base material, when cooled from a high temperature range, begins to undergo a phase transformation from the austenite phase to the ferrite phase at some point in the temperature range of approximately 850 to 950°C. As a result of the inventors' investigations, it has been revealed that the deformation resistance of the Fe-based alloy base material changes significantly at a temperature within the temperature range of approximately 850 to 950°C, which is thought to correspond to the temperature at which the phase transformation from the austenite phase to the ferrite phase occurs. In other words, with the boundary temperature in the range of 850 to 950°C as the dividing line, in the temperature range on the higher side, which is thought to be the austenite phase region, the deformation resistance is generally equivalent to that of the Ni-based metal, although this depends on the type of Ni-based metal used in the bonding material. On the lower side, where the ferrite phase is thought to begin to form, the deformation resistance decreases significantly, creating a difference in deformation resistance between the Ni-based metal and the bonded material. 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 (bonded material), and thus affect the variation in the thickness of the bonded material, i.e., the standard deviation. Therefore, it is considered necessary to appropriately control the rolling rate above 950°C, which is less likely to produce variations in thickness, by specifying the above-mentioned equations 5 to 7 according to the standard deviation of the thickness of the materials before rolling and bonding.

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

[0065] [Clad Manufacturing] (1) Cladding manufacturing 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. As the material for the first layer of each clad, or the third layer of the three-layer clad, a plate of pure nickel NW2201 or Ni-based alloy NCF600 with a width and length of 150.0 mm was prepared, and as the material for the second layer, carbon steel SPCE with the thickness shown in Table 1 and a width and length of 150.0 mm was prepared. Each material was manufactured as follows.

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

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

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

[0069] For each material, the thickness was measured using calipers at 10 points, 30 mm from the edge of the board width and 10 mm apart from each other, centered on the middle of the board length, and the standard deviation s was determined. Ｎｉ１ s Ｆｅ s Ｎｉ２ The calculations were performed. Subsequently, in the case of a two-layer cladding, the materials for the first and second layers were stacked in this order, and in the case of a three-layer cladding, the materials for the first, second, and third layers were stacked in this order. The four periphery of each material interface was then fixed by covered arc welding to create a two-layer or three-layer laminate.

[0070] These laminates were subjected to rolling bonding with varying heating temperatures T [°C] and pass schedules to produce hot-rolled sheets with a total thickness of 5.0 mm, in which each layer was integrated. During this process, the heating temperature before rolling and the rolling rate r of the first pass were varied. １ , the rolling rate r until the rolling pass in which the laminate temperature falls below 950°C ９５０ Measure the value K expressed by the following formulas 9 to 13. １ _K ２ , L Ｎｉ１ , L Ｆｅ , L Ｎｉ２ I calculated K. １ =-0.00068×T+0.936 Formula 9 K ２ =-0.00059×T+0.812 Formula 10 L Ｎｉ１ = s Ｎｉ１ × (1-r ９５０ ) Formula 11 L Ｆｅ = s Ｆｅ × (1-r ９５０ ) Formula 12 L Ｎｉ２ = s Ｎｉ２ × (1-r ９５０ ) Equation 13

[0071] Under the same conditions thereafter, cold rolling with a rolling ratio of 80% and annealing at 850°C were performed to prepare clad samples rolled to a thickness of 1.0 mm.

[0072] Table 1 shows the details and manufacturing conditions of each clad sample prepared. Underlined text in each table indicates that it is outside the scope of this disclosure.

[0073]

[0074] For these cladding samples, 15 mm wide and long plate cross-sectional observation samples were prepared at 10 different locations, each more than 50 mm apart, with the L-shaped cross-section as the observation surface. The thickness of the first and third layers was measured at 10 points per observation sample. To calculate the standard deviation and average thickness from the data for each layer thickness from these 100 points, the L-shaped cross-sections were observed, and the average thickness e [mm] and standard deviation s of the first layer were determined. １ , the average thickness f [mm] of the second layer and the standard deviation s ２ , the average thickness g [mm] of the third layer and its standard deviation s ３The following was measured. Then, from the data of the thickness of each layer, the ratio t of the average thickness of the first layer when the total thickness of the cladding is set to 1 was calculated. １ , the ratio of the average thickness of the second layer t ２ , the ratio of the average thickness of the third layer t ３ The following value H was calculated by performing the calculation and determining the value H defined by equation 14 below. H = (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 ) Equation 14 Here, d １ The density of the first layer [g / cm³] ３ ), d ２ The density of the second layer [g / cm³] ３ ), d ３ The density of the third layer [g / cm³] ３ ] [Ni] １ This is the mass ratio of Ni per unit mass of the first layer, [Ni] ２ This is the mass ratio of Ni per unit mass of the second layer, [Ni] ３ This is the mass percentage of Ni per unit mass of the third layer. Note that NW2201, NCF600, and SPCE used as materials were all cut from a single block, and the density d of each layer was determined from the measurement results of each block. １ d ２ d ３ The values ​​were set to 8.88 if the material of the layer was NW2201, 8.40 if it was NCF600, and 7.85 if it was SPCE. In addition, the mass percentage of Ni per unit mass of each layer was set to 0.995 if the material of the layer was NW2201, 0.770 if it was NCF600, and 0.000 if it was SPCE.

[0075] [Evaluation] (Corrosion resistance in alkaline environments) A 1.0 mm thick clad cold-rolled sheet sample was cut in half along its width using a shear. The cross-sections of the shears were fixed together, and arc welding was performed manually along the line where they met. ENi2061 (JIS Z 3224:2010), a covered arc welding rod, was used as the welding rod. After welding, three prismatic samples measuring 1.0 mm × 1.0 mm × 30 mm were cut from the weld metal at different locations. After measuring the mass and calculating the density, the samples were subjected to an immersion test in a high-temperature alkaline solution. The collected prismatic samples were degreased and washed, their mass was measured before the immersion test, and they were immersed in a 48% NaOH aqueous solution at 90°C for 24 hours. After that, the samples were washed again, and their mass was measured after the immersion test. The corrosion rate [m / s] was calculated from the mass change before and after the immersion test. At this time, the corrosion rate for all three prismatic samples was 3.5 × 10 －１３ If the value is less than [m / s], the corrosion resistance of the weld metal (weld bead) is good (Y), and even a single prismatic sample is 3.5 × 10 －１３ If the value 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 that were prepared and the results of the corrosion resistance evaluation.

[0076]

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

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

Claims

1. A two-layer structure comprising a first layer made of pure nickel or a Ni-based alloy, and a second layer bonded to one surface of the first layer and made of an Fe-based alloy, or a three-layer structure further comprising a third layer bonded to the surface of the second layer opposite to the surface bonded to the first layer and made of pure nickel or a Ni-based alloy, wherein 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 , s １ and s ３ are each 60 [μm] or less, and the clad 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 Formula (I) In the formula (I), t １ is the ratio of the average thickness of the first layer when the average total thickness of the clad is taken as 1, t ２ is the ratio of the average thickness of the second layer when the average total thickness of the clad is taken as 1, t ３ is the ratio of the average thickness of the third layer when the average total thickness of the clad is taken as 1, d １ is the density [g / cm ３ , d ２ is the density [g / cm ３ , d ３ is the density [g / cm ３ , [Ni] １ is the mass proportion of Ni per unit mass of the first layer, [Ni] ２ is the mass proportion of Ni per unit mass of the second layer, [Ni] ３ is the mass proportion 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 Let each of these values ​​be 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 according to claim 1 or claim 2, having the two-layer structure, wherein the first layer is pure nickel.

4. The cladding according to claim 1, having the three-layer structure, wherein 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.

5. The cladding according to claim 1 or claim 4, having the three-layer structure, wherein at least one of the first layer and the third layer is pure nickel.

6. The cladding according to any one of claims 1 to 5, wherein the average of the total thickness is greater than 0.1 mm and 3.0 mm or less.

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