Clad plate

Abstract

A clad plate having: a first layer that comprises a stainless steel; a second layer that is bonded to the first layer, and comprises pure aluminum or an aluminum alloy; and a first oxide layer that is present between the first layer and the second layer at least in a partial manner, wherein the percentage of interposition of the first oxide layer at the interface between the first layer and the second layer is 95.0% or greater.

Description

[Technical Field]

[0001] The present disclosure relates to clad plates. [Background technology]

[0002] Clad plates made by joining different types of metals (hereinafter referred to as "dissimilar metals") together using methods such as rolling or pressure welding combine the excellent properties of each of the constituent dissimilar metals in a highly balanced manner, giving them new properties that cannot be achieved with single metals or alloys.

[0003] Materials used in the sliding parts of machine parts must have high wear resistance to withstand strong sliding, as well as high thermal conductivity to efficiently dissipate heat generated by friction. Among these are sliding components used under harsh operating conditions, such as brake rotors used to slow down rotating parts, which require both high wear resistance and high thermal conductivity for the sliding surface. Furthermore, if the material is used in a harsh corrosive environment, such as outdoors, the material itself must also be corrosion resistant.

[0004] Conventional sliding parts, such as rotor plates and clutch plates, are mainly made of single plates, such as wear-resistant steel or stainless steel. However, as mentioned above, it is difficult to apply a single material to sliding parts that require high levels of various properties, such as wear resistance, thermal conductivity, and corrosion resistance. For example, stainless steel has excellent strength, sliding properties, and corrosion resistance, but poor thermal conductivity. On the other hand, aluminum and aluminum alloys, which have excellent thermal conductivity, have poor strength, wear resistance, and high-temperature strength when heated by frictional heat. Therefore, it is effective to use clad plates that combine various properties to a high degree by layering materials with different properties.

[0005] Patent Document 1 discloses a clad thin plate in which an outer layer is made of hardened carbon steel or martensitic stainless steel, which has high strength and wear resistance, and an inner layer is made of an aluminum alloy, which has high thermal conductivity.

[0006] Patent Document 2 also discloses a clad in which two or more layers of different metal materials are laminated in the plate thickness direction, and one or both surface layers of the metal material are stainless steel with a thickness of 0.03 mm or more, and the average nitrogen content in the stainless steel layer in the region from both ends in the thickness direction to 0.01 mm is 0.01 to 0.3 mass %, and the average nitrogen content in the region from both ends in the thickness direction to 0.01 mm in the stainless steel layer is 1.3 times or less the average nitrogen content in the region from the center in the thickness direction to ±0.005 mm.

[0007] Patent Document 3 discloses a clad having a two-layer structure of stainless steel and aluminum, or a three-layer structure of stainless steel, aluminum, and stainless steel, in which the clad has a tensile strength of 200 to 500 MPa, an elongation of 15% or more, a surface hardness of the stainless steel layer of HV300 or less, an average crystal grain size of 15 to 10 μm, and in a cross-sectional observation image from a plane perpendicular to the rolling direction (C-section), the number of shear bands crossing a 10 μm long line parallel to the plate thickness direction is less than 5. These have excellent formability and heat dissipation properties, which are required for electronic devices such as smart devices.

[0008] Furthermore, Patent Document 4 discloses a clad plate for use in induction heating (IH) electromagnetic cookware, which is made by cold rolling and pressure welding a ferritic stainless steel plate that provides IH heat generation and surface corrosion resistance with pure aluminum or an aluminum alloy that provides heat conductivity, which has the advantage of allowing heat to be distributed throughout the cookware.

[0009] Patent Document 5 also discloses a method for manufacturing a clad, which is characterized by the fact that in the process of joining two different materials, heating is performed using an infrared lamp from the side of the metal strip that requires a relatively greater amount of annealing, and the side of the metal strip that requires a relatively lesser amount of annealing is cooled by contacting it with a water-cooled plate, thereby achieving the purpose of annealing while preventing the formation of intermetallic compounds at the joining surface of the two metals.

[0010] Patent Document 1: Patent No. 6119942 Patent Document 2: JP 2021-154335 A Patent document 3: Re-table 2017 / 057665 publication Patent Document 4: Japanese Patent Application Laid-Open No. 7-223081 Patent Document 5: Japanese Patent Application Laid-Open No. 9-182981 Summary of the Invention [Problem to be solved by the invention]

[0011] As described above, clad plates suitable for applications requiring a variety of properties are being used in a variety of applications and are becoming increasingly widespread. However, when clad plates, particularly those disclosed in Patent Documents 1 to 5, which are made of a layer of a steel material such as stainless steel and a layer of aluminum, are continuously exposed to high temperatures above a certain level, dissimilar metals react at the interface between the layers, producing brittle intermetallic compounds. Then, interfacial peeling occurs starting from the generated site, which may result in a decrease in peel strength.

[0012] Therefore, an object of the present disclosure is to provide a clad plate whose peel strength is less likely to decrease even when repeatedly exposed to high temperature conditions. [Means for solving the problem]

[0013] Means for solving the above problems include the following aspects. <1> a first layer made of stainless steel; a second layer bonded to the first layer and made of pure aluminum or an aluminum alloy; a first oxide layer present between the first layer and the second layer; and A clad plate, wherein the proportion of the first oxide layer present at the interface between the first layer and the second layer is 95.0% or more. <2> a third layer made of stainless steel and joined to the second layer on the opposite side to the first layer; a second oxide layer present between the second layer and the third layer; and The proportion of the second oxide layer present at the interface between the second layer and the third layer is 95.0% or more. <1> The clad plate according to claim 1. <3> The stainless steel is a martensitic stainless steel. <1> or <2> The clad plate according to claim 1. <4> The total thickness is more than 0.1 mm <1> ~ <3> The clad plate according to any one of claims 1 to 10. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide a clad plate whose peel strength is unlikely to decrease even when repeatedly exposed to high temperatures. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an explanatory diagram showing the overall configuration of an example of a clad plate according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0016] An example of the present disclosure will be described below. In the present disclosure, the "%" designation for the content of each element in the chemical composition means "mass %." When the lower limit of the content of each element in the chemical composition is expressed as "0", this means that the element is an optional component and does not need to be contained. In a numerical range expressed using "to", when the numbers before and after "to" are not followed by "greater than" or "less than", it means a range that includes those numbers as the lower and upper limits. Furthermore, when the numbers before and after "to" are followed by "greater than" or "less than", it means a range that does not include those numbers as the lower or upper limits. In numerical ranges described in stages, the upper limit of a certain numerical range may be replaced by the upper limit of another numerical range described in stages, or may be replaced by a value shown in an example. Also, the lower limit of a certain numerical range may be replaced by the lower limit of another numerical range described in stages, or may be replaced by a value shown in an example. 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.

[0017] The clad plate according to the present disclosure has a first layer made of stainless steel, a second layer made of pure aluminum or an aluminum alloy bonded to the first layer, and a first oxide layer present at least partially between the first and second layers. The proportion of the first oxide layer present at the interface between the first layer and the second layer is 95.0% or more.

[0018] The clad plate according to the present disclosure, due to the above-described configuration, is less likely to exhibit a decrease in peel strength even when repeatedly exposed to high temperatures. The clad plate according to the present disclosure was discovered based on the following findings.

[0019] The inventors have investigated the peel strength of clad plates when repeatedly exposed to high temperatures, and have found the following.

[0020] (A) In the joining rolling process of clad plates made of stainless steel and aluminum plates, the dissimilar metals that form the raw materials are heated, which causes a thin oxide film to form on the surface of each material. (B) The oxide film formed in the bonding roll-forming process remains as an extremely thin intermediate layer (hereinafter referred to as oxide layer) with a thickness of about 10 nm at least on a part of the interface even after bonding. (C) It has been known that when manufacturing clad plates made of dissimilar metals, some oxides remain. It has been thought that bonding at the interface between the layers is ensured by bonding between the dissimilar metals at locations where no oxide layer is present, which is formed when the oxide layer is destroyed by the elongation of the dissimilar metal materials during rolling. However, as a result of research by the inventors, it has been found that when joining specific dissimilar metals using the bonding rolling method, the dissimilar metals are joined not only by bonding between the metals themselves, but also through an oxide layer of a certain thickness that originates from the oxide layer on the surface of each material. (D) In ​​conventional inventions, when a clad made of dissimilar metals is manufactured, the largest constituent element of the material of each opposing metal layer may be concentrated beyond the interface of each metal layer, sandwiching an oxide layer at the joining interface made of oxide. (E) In the prior art, particularly when the metal layers are one layer made of stainless steel (hereinafter also referred to as "stainless steel layer") and the other layer made of pure aluminum or an aluminum alloy (hereinafter also referred to as "aluminum layer"), Fe, which is the largest constituent element of the paired stainless steel layer, diffuses from the stainless steel layer across the interface with the aluminum layer to the aluminum layer side and becomes concentrated. In clad plates such as those described in (F) and (E), if Fe is concentrated on the aluminum layer side near the interface with the stainless steel layer, the peel strength decreases when exposed to high temperatures of around 500°C. (G) On the other hand, according to the study by the inventors, if the concentration of Fe on the aluminum layer side can be suppressed, the decrease in peel strength can be suppressed even after exposure to a high temperature of about 500°C. (H) The concentration of Fe on the aluminum layer side can be suppressed by increasing the proportion of the oxide layer present at the interface between the stainless steel layer and the aluminum layer.

[0021] From the above findings, it has been discovered that the clad plate according to the present disclosure is less likely to experience a decrease in peel strength even when repeatedly exposed to high temperatures.

[0022] The clad plate according to the present disclosure will be described in detail below.

[0023] 1. Clad plate according to the present disclosure (1) Overall structure FIG. 1 is an explanatory diagram showing the overall configuration of an example of a clad plate according to the present disclosure. As shown in FIG. 1, the clad plate 1 includes a first layer 2, a second layer 3, and a third layer 4. However, the third layer 4 is a layer that is provided arbitrarily as needed.

[0024] The second layer 3 has a pair of front and back surfaces facing each other in the layer thickness direction, one of which is bonded to the first layer 2 and the other of which is bonded to the third layer 4. Between the first layer 2 and the second layer 3 there is at least partially present a first oxide layer. If the third layer 4 is present, it has a second oxide layer present at least partially between the second layer 3 and the third layer 4 . That is, the first oxide layer and the second oxide layer are present partially or entirely at the interface between the first layer 2 and the second layer 3, and at the interface between the second layer 3 and the third layer 4, respectively.

[0025] The first oxide layer and the second oxide layer are not shown in FIG.

[0026] Here, for example, in a plate material made of a single layer of stainless steel, if a localized high-temperature area occurs, such as the sliding portion of a sliding part or the heat-generating portion of an induction cooker, the heat from that area is difficult to dissipate, and the sliding portion or the heat-generating portion becomes excessively hot, causing severe high-temperature wear or high-temperature corrosion. On the other hand, a plate material made of a single layer of pure aluminum or an aluminum alloy has a higher thermal conductivity than a plate material made of a single layer of stainless steel, but has lower strength, wear resistance, and corrosion resistance. For example, it is difficult to use a single-layer plate material as a component that requires high wear resistance, such as a sliding component, or as a structural component that requires high corrosion resistance, such as a cooking utensil.

[0027] Therefore, the clad plate 1 according to the present invention is a clad plate consisting of two layers, a first layer 2 and a second layer 3, each having different properties, or three layers, a first layer 2, a second layer 3, and a third layer 4, each having different properties. Specifically, this is as follows.

[0028] (2) Layer 1 2 and Layer 3 4 The first layer 2 and the third layer 4 are layers made of stainless steel. The first layer 2 and the third layer 4 may be made of different materials or industrially the same material within the category of layers made of stainless steel.

[0029] The type of stainless steel constituting the first layer 2 and the third layer 4 is not particularly limited, and examples thereof include ferritic stainless steel, austenitic stainless steel, martensitic stainless steel, austenitic-ferritic duplex stainless steel, and precipitation-hardened stainless steel. Specific examples of the type of stainless steel include SUS304 (austenitic stainless steel), SUS316 (austenitic stainless steel), SUS301 (austenitic stainless steel), SUS302 (austenitic stainless steel), SUS403 (martensitic stainless steel), SUS430 (ferritic stainless steel), SUS329J1 (austenitic-ferritic duplex stainless steel), and SUS821L1 (austenitic-ferritic duplex stainless steel), which are specified in JIS G 4304:2015 or JIS G 4305:2015. Among these, martensitic stainless steel is preferable because of its high wear resistance.

[0030] (3)Second layer 3 The second layer 3 is a layer made of pure aluminum or an aluminum alloy. Pure aluminum is an aluminum material that does not contain intentionally added elements and is composed of impurities and Al, and typically has an Al content of 98% by mass or more. Specific examples include A1050, A1060, and A1100, as specified in JIS H 4000:2014. Examples of impurities include Si, Fe, Cu, Mn, Cr, Zr, Ga, V, N, Ni, B, and Ti. The aluminum alloy sheet is not particularly limited in type, and may be any commonly used alloy, including 2000 series Al-Cu alloys, 3000 series Al-Mn alloys, 4000 series Al-Si alloys, 5000 series Al-Mg alloys, 6000 series Al-Mg-Si alloys, and 7000 series Al-Zn-Mg alloys. Specific examples include A2017 (2000 series), A2024 (2000 series), 3003A (3000 series), 3004 (3000 series), A4032 (4000 series), A5052 (5000 series), A5083 (5000 series), A6063 (6000 series), A6N01 (6000 series), A6061 (6000 series), A7075 (7000 series), and A7N01 (7000 series), as specified in JIS H 4000:2014.

[0031] (4) First oxide layer and second oxide layer The first oxide layer and the second oxide layer are respectively partially or entirely interposed between the first layer 2 and the second layer 3, and between the second layer 3 and the third layer 4 (hereinafter, these are also referred to as metal layer interfaces). The first layer 2 and the second layer 3, and the second layer 3 and the third layer 4 are bonded via the first oxide layer and the second oxide layer, respectively.

[0032] The first oxide layer and the second oxide layer are mainly the remaining oxides formed on the surface layers of the first layer 2, the second layer 3, and the third layer 4 by heating before clad roll bonding. Therefore, the first oxide layer and the second oxide layer are each made up of surface oxides formed when the material is heated, and in particular, the surface oxide of pure aluminum or aluminum alloy derived from the second layer 3 accounts for the majority of them.

[0033] The proportion of the first oxide layer and the second oxide layer present at the interface with the metal layer (i.e., the proportion of the first oxide layer present at the interface between the first layer and the second layer, and the proportion of the second oxide layer present at the interface between the second layer and the third layer) is 95.0% or more, more preferably 97.0% or more, and even more preferably 100.0%. If the oxide layer is too thin, it may not be possible to suppress the diffusion of Fe toward the aluminum layer, so the thickness of the oxide layer is preferably 3 nm or more, more preferably 4 nm or more, and even more preferably 5 nm or more. On the other hand, if the oxide layer is made thicker than necessary, the heating temperature must be increased during the annealing and rolling-bonding processes, which increases energy costs. Furthermore, if the oxide layer is made thicker than necessary, the oxide film formed on the surface of each material, particularly during the rolling-bonding process, may actually hinder roll-bonding. Therefore, the thickness of the oxide layer is preferably 200 nm or less, and more preferably 100 nm or less. In addition, the thickness of the oxide layer is the thickness of the first oxide layer in the case of a clad plate having a first layer 2 and a second layer 3, and is the average thickness of the first oxide layer and the second oxide layer in the case of a clad plate having a first layer 2, a second layer 3, and a third layer 4.

[0034] The presence of the first oxide layer and the second oxide layer at the metal layer interface (i.e., the first oxide layer at the interface between the first layer and the second layer, and the second oxide layer at the interface between the second layer and the third layer) at a rate of 95.0% or more suppresses the concentration of the largest constituent element (i.e., Fe) of the first layer 2 and the third layer 4 in the vicinity of the interface of the second layer 3. As a result, even when repeatedly exposed to high temperatures, the decrease in the peel strength at the interface between the first layer 2 and the second layer 3 and the interface between the second layer 3 and the third layer 4 is suppressed. The reason for this is still unknown and remains a matter of speculation, but the reasons described below are thought to be the case.

[0035] That is, the presence of the oxide layer at the metal layer interface suppresses the diffusion and movement of metal elements across the interface, which is thought to have the effect of suppressing the diffusion of Fe, the largest constituent element of the first layer 2 and the third layer 4, from the first layer 2 and the third layer 4 to the second layer 3 when exposed to high temperatures, thereby suppressing the generation of Fe-Al based intermetallic compounds. Fe-Al based intermetallic compounds are highly brittle and may become the starting point for fracture during bending and other processes, which is thought to lead to a decrease in joint strength during processing.

[0036] The proportion of the first oxide layer and the second oxide layer present at the interface with the metal layer, and the thicknesses of the first oxide layer and the second oxide layer are measured as follows.

[0037] A thin film test piece is prepared from the clad plate to be measured along a cross section (TD plane) perpendicular to the plate width direction, including the metal layer interface, using a FIB (FOCUSED ION BEAM) device.

[0038] Using a FE-TEM (Field Emission Transmission Electron Microscopy) equipped with EDX (Energy Dispersive X-ray Spectroscopy), a cross section of the thin film specimen, including the metal layer interface, was observed using EDX area analysis at a magnification of 50,000x and a field of view of 1.0 x 1.0 μm, and the oxide layer present at the metal layer interface was identified. Here, the EDX area analysis identified regions with an oxygen content of 5% or more in atomic percent as the oxide layer. From the observation results, the ratio of the length of the oxide layer to the length of the metal layer interface in the field of view was calculated. This operation is carried out for 10 fields of view at 1.0 μm intervals, and the arithmetic mean of the ratio of the length of the oxide layer to the length of the metal layer interface is calculated, which is the ratio of the oxide layer interposed in the metal layer interface.

[0039] The thickness of the oxide layer is measured as follows. First, the length of the region where the oxygen content is 5% or more is measured in atomic percent by EDX analysis along the thickness direction (ND direction). This operation is performed at five locations at 5 μm intervals, and the arithmetic average of the lengths of the regions where the oxygen content is 5% or more is calculated, which is the thickness of the oxide layer. Here, in the case of a clad plate 1 having a first layer 2, a second layer 3, and a third layer 4, a thin film test piece including the metal interface between the first layer 2 and the second layer 3, and the metal interface between the second layer 3 and the third layer 4 is prepared, and the average value of the first oxide layer and the second oxide layer is calculated to be the thickness of the oxide layer.

[0040] The analytical conditions for the EDX analysis are as follows: measurement elements: O, Fe, Cr, Ni, Mn, Mg, Al, and Si; acceleration voltage: 200 kV; detection time: 1 minute; probe diameter: 4 nm or less.

[0041] (6) Total thickness The total thickness of the clad plate 1 according to the present disclosure is preferably more than 0.1 mm. By making the total thickness of the clad plate 1 more than 0.1 mm, sufficient rigidity can be ensured in environments where it is required as a high-performance sliding member, cooking utensil, or electronic device housing. From the viewpoint of rigidity, the total thickness of the clad plate 1 is more preferably 0.3 mm or more, even more preferably more than 0.5 mm, and even more preferably 0.8 mm or more. On the other hand, from the viewpoint of the use of the clad plate and the material cost, the upper limit of the total thickness of the clad plate 1 is preferably 3.0 mm, more preferably 2.5 mm, and still more preferably 2.0 mm. The thickness of each layer constituting the clad plate 1 may be set appropriately in consideration of the performance required for the intended use, within a range not falling below the preferred lower limit of the total thickness mentioned above.

[0042] 2. Manufacturing method of clad plate 1 A preferred method for manufacturing the clad plate 1 according to the present disclosure will now be described.

[0043] The clad plate 1 according to the present disclosure can achieve the effects described above regardless of the manufacturing method, but the following method is preferred because it allows stable manufacturing.

[0044] The clad plate 1 according to the present disclosure can be manufactured through a stainless steel material annealing process, a lamination process, a rolling process, and a heat treatment process. In particular, the manufacturing of the clad plate 1 of the present disclosure is significantly affected by the annealing process of the stainless steel material as a pretreatment process for the lamination and rolling processes. The heat treatment process may be omitted depending on the application. The shape and finish of the material for each layer are not important, but using coiled thin plates is preferable because it allows for continuous heating, lamination, and roll bonding, improving production efficiency.

[0045] [Stainless steel material annealing process] This is a process in which the stainless steel material that forms the first layer 2 and the third layer 4 is brush polished and bright annealed under specified conditions. [Lamination process] A process in which the stainless steel material, which is the material for the first layer 2 and the third layer 4, that has been subjected to a stainless steel material annealing process, and the aluminum material or aluminum alloy material, which is the material for the second layer 3, are heated, and the stainless steel material, which is the material for the first layer 2, the aluminum material or aluminum alloy material, which is the material for the second layer 3, and the stainless steel material, which is the material for the third layer 4, are stacked in this order to form a laminate. [Rolling process] A step of joining and rolling the laminate that has been through the laminating step to form a clad plate (1) having a first layer (2), a second layer (3), and a third layer (4). [Heat treatment process] A process of subjecting the clad plate 1 that has been subjected to the rolling process to heat treatment by holding it at 300 to 450°C for 3 minutes or more.

[0046] Each step will be explained below in order.

[0047] (1) Stainless steel material annealing process In the stainless steel material annealing step, it is preferable to subject the stainless steel material, which is the material for the first layer 2 and the third layer 4, to a preliminary heat treatment by brush polishing and bright annealing before lamination and rolling. Specifically, this is as follows.

[0048] First, a stainless steel material in the form of a plate or a stainless steel material coil in the form of a strip is prepared by casting, hot rolling, cold rolling, or the like. Next, the plate-shaped stainless steel material or the strip-shaped stainless steel material coil is brush-polished, if necessary, on either the front or back surface that will be the joining surface. The conditions for brush-polishing may be changed depending on the properties of the clad plate 1, or it may be omitted. However, if brush-polishing is to be performed, it should be performed before bright annealing.

[0049] Next, bright annealing is performed. There are several methods for annealing stainless steel materials before joining, but bright annealing is preferred. By performing bright annealing under specified conditions, the clad plate 1 according to the present disclosure can be stably produced.

[0050] Here, bright annealing refers to annealing carried out in an inert or reducing atmosphere in order to minimize surface oxidation of the stainless steel material. The stainless steel material is preferably produced under the following conditions. The annealing atmosphere is preferably an inert gas such as Ar or a gas containing reducing hydrogen. In terms of production costs, ammonia decomposition gas consisting mainly of nitrogen and hydrogen may also be used. The bright annealing temperature is preferably in the range of 900 to 1100°C from the viewpoint of ensuring a balance between the tensile strength and elongation of the clad plate 1 after bonding. From the viewpoint of the surface properties of the stainless steel material, the dew point of the bright annealing atmosphere is preferably −50° C. or lower, more preferably −55° C. or lower, to prevent excessive oxidation. On the other hand, an excessive decrease in the dew point leads to an increase in production costs, so the dew point is preferably −80° C. or higher, more preferably −75° C. or higher.

[0051] Bright annealing is preferably carried out under conditions that satisfy the following formula 1, where t (s) is the annealing time. 7.429×10 6 ×T -1 ×|D| -0.8993 ≦ t ≦ 7.791×10 6 ×T -1 ×|D| -0.8724 ...Formula 1 Here, T (°C) is the bright annealing temperature, and D (°C) is the dew point at the bright annealing temperature. The bright annealing time t is calculated by dividing the left side of Equation 1 by 7.429 × 10 6 ×T -1 ×|D| -0.8993 " or more, the ratio of the oxide layer falls within the above range. On the other hand, if the bright annealing time is too long, not only will the manufacturing cost increase, but the ratio of the oxide layer to the entire dissimilar metal interface will decrease. This is thought to be because, as will be described later, the strong Cr oxide film, which is mainly composed of Cr, becomes thinner than necessary due to reduction. Therefore, the right-hand side of Equation 1, "7.791 × 10 6 ×T -1 ×|D| -0.8724 " or less is preferable.

[0052] (2)Lamination process In the lamination process, first, the stainless steel material that is the material for the first layer 2, the pure aluminum material or aluminum alloy material that is the material for the second layer 3, and the stainless steel material that is the material for the third layer 4 are heated separately and then laminated in this order to form a laminate. In the stainless steel material annealing process, when the stainless steel material that is the material for the first layer 2 and the third layer 4 is subjected to brush polishing, the stainless steel material is stacked so that the polished surface faces the joining surface of the pure aluminum material or aluminum alloy material that is the material for the second layer 3.

[0053] The heating temperature of the materials for each layer in the lamination process is preferably 150°C or higher to ensure bonding in the next rolling process. However, excessive heating not only increases manufacturing costs but also causes uneven temperature distribution during heating of the materials being passed through, affecting the bonding strength. In particular, there is a risk of a decrease in strength in the aluminum layer. This may also result in warping or shrinkage during rolling. Therefore, the heating temperature is preferably 350°C or lower. From the viewpoints of ensuring a good bonding state during rolling and manufacturing costs, the heating temperature is more preferably 170°C or higher and 300°C or lower.

[0054] (3) Rolling process In the rolling process, the stainless steel material that is the material for the first layer 2, the pure aluminum material or aluminum alloy material that is the material for the second layer 3, and the stainless steel material that is the material for the third layer 4 in the laminate are joined together, and the laminate is rolled to form the shape of a clad plate.

[0055] If the rolling ratio in the rolling step is less than 10%, there is a risk that bonding at the interface of the metal layers may not progress sufficiently, so the rolling ratio is preferably 10% or more. From the viewpoint of achieving sufficient bonding, the rolling ratio is more preferably 13% or more, even more preferably 15% or more, and even more preferably 17% or more. There is no upper limit to the rolling ratio in the rolling step, but from the viewpoint of increasing the load on the rolling mill and making it difficult to ensure the product shape, it is preferably 60% or less, more preferably 55% or less, and even more preferably 50% or less. The rolling reduction ratio (%) is calculated by 100×{(thickness of laminate)−(thickness of clad plate)} / (thickness of laminate).

[0056] (4) Heat treatment process In the heat treatment step, heat treatment is performed to recover as much as possible the processing strain introduced into the clad plate 1 by the rolling step and to improve workability. If the application does not require high workability, this step may be omitted.

[0057] The lower limit of the heat treatment temperature depends on the application and is not particularly set, but if the workability of the clad plate 1 is to be ensured to a certain extent, the heat treatment temperature is preferably 150°C or higher. From the viewpoint of ensuring workability, the heat treatment temperature is more preferably 200°C or higher. On the other hand, if the heat treatment temperature exceeds 500°C, the oxide disappears and an Fe-Al intermetallic compound is formed at the interface, and the oxide layer is not interposed at the interface, making the interface embrittled and reducing the bonding strength. The heat treatment temperature is more preferably 220°C or higher. Furthermore, the heat treatment temperature is preferably 400°C or lower.

[0058] The heat treatment time is preferably 3 minutes or more, and more preferably 10 minutes or more, in order to ensure workability. Although there is no upper limit to the heat treatment time, it is preferably 50 hours or less from the viewpoint of the energy cost involved in annealing.

[0059] Through the above steps, the clad plate 1 according to the present disclosure can be stably manufactured. It is still unclear how the manufacturing conditions in bright annealing affect the suppression of diffusion at the metal layer interface of the clad plate 1 sandwiching the oxide layer, and this is only speculation, but factors such as those described below are thought to be involved.

[0060] When materials with different strengths are joined by rolling, plastic flow of the materials occurs at the interface between the metal layers, and the materials of each metal layer elongate. At this time, in parts near the surface of each metal layer, some of the oxide layers, which have low adhesion to the surface of the material, are thought to mix with the structure of the surface of each metal layer, becoming mixed as metal or metal oxide, or becoming solid-solubilized in the structure, resulting in partial loss of the layered oxide. Furthermore, plastic flow and elongation of the materials of each metal layer during rolling cause fracture of the brittle oxide layers, and in those areas, the metals of each layer are thought to be partially joined without the oxide layer.

[0061] In particular, the Fe-Cr oxide film formed by atmospheric oxidation from the lamination process to the roll-bonding process has lower adhesion to the base material and is more brittle than the Cr oxide film described below. Therefore, it is likely to peel off from the base material and become caught in the plastic flow that occurs in soft materials. Furthermore, it is thought that in areas where the Fe-Cr oxide has formed, the oxide layer is partially destroyed due to its high brittleness.

[0062] On the other hand, bright annealing under appropriate conditions is thought to preferentially form a Cr oxide film on the surface of stainless steel. The Cr oxide film formed by bright annealing is strong and extremely thin, comparable to or slightly thicker than a passive film, and is thought to suppress atmospheric oxidation that occurs during warm roll joining to a certain extent, thereby suppressing the formation of the Fe-Cr oxides mentioned above.

[0063] Furthermore, due to its high adhesion to the substrate, the Cr oxide film formed by bright annealing is likely to remain as an intermediate layer after bond-rolling. Therefore, during the heat treatment process after bond-rolling and when exposed to high temperatures during use, the Cr oxide film acts as an oxide layer at the uniform, seamless interface between the dissimilar metals, suppressing the diffusion of Fe atoms into the aluminum layer and suppressing the formation of Fe-Al intermetallic compounds. This mechanism is thought to suppress delamination at the metal layer interface of the clad plate 1 during processing.

[0064] On the other hand, excessively lowering the dew point, increasing the annealing temperature, and lengthening the annealing time not only lead to a significant increase in manufacturing costs, but also reduce the thickness of the strong and dense Cr oxide film formed during bright annealing of the stainless steel material in a reducing atmosphere, which may result in an insufficient oxide layer when the clad plate 1 is made, or the oxide layer may be broken due to elongation of the material. It is presumed that at the points where the metals are directly joined in this way, Fe elements diffuse across the interface between the stainless steel and aluminum layers and into the aluminum layer under high-temperature conditions, promoting the formation of an Fe-Al intermetallic compound. [Example]

[0065] The effects of the present disclosure will be explained below using examples, but the present disclosure is not limited to the conditions used in the following examples.

[0066] The materials used for the first and third layers of the clad plate were either ferritic stainless steel plate SUS430, austenitic stainless steel plate SUS304, or martensitic stainless steel plate SUS403, and the material used for the second layer was pure aluminum plate A1100 or aluminum alloy plate A3004. The order of lamination was set to be the first layer material, then the second layer material, and finally the third layer material, meaning that the stainless steel plate was the surface layer of the clad plate, and the aluminum plate was the middle layer sandwiched between the two surface layers. For some samples, only the first and second layers were laminated together. The thickness of the material for the first layer and the material for the third layer was 0.55 mm, and the thickness of the material for the second layer was 1.4 mm. In the rolling process, the layers were rolled to the thicknesses described below.

[0067] First, the stainless steel sheet used for the first and third layers was subjected to bright annealing. Ammonia decomposition gas was used as the annealing atmosphere. The annealing temperature, annealing atmosphere dew point, and annealing time during bright annealing were varied for each sample. The values ​​of the annealing temperature T (°C) and annealing atmosphere dew point D (°C) were used to calculate the A value in Equation 2 and the B value in Equation 3 below. A = 7.429 × 10 6 ×T -1 ×|D| -0.8993 ...Formula 2 B = 7.791×10 6 ×T -1 ×|D| -0.8724 ...Formula 3

[0068] Next, the bright annealed first and third layer materials and the second layer material were used to laminate the first layer material, the second layer material, and the third layer material, or if only the first and second layers were used, the first layer material and the second layer material, in that order, and the laminate was heated to 200°C and warm-rolled. The rolling reduction was 20%. This bonded assembly was then heat-treated at various temperatures for 30 minutes to produce clad plate test pieces with a total thickness of 1.5 to 2.0 mm.

[0069] The prepared clad plate test pieces were subjected to the following investigations and evaluations according to the methods already described.

[0070] -Characteristics- The proportion of the first oxide layer present at the interface between the first and second layers (referred to as "proportion of the first oxide layer" in the table) The proportion of the second oxide layer present at the interface between the first and second layers (referred to as "proportion of the second oxide layer" in the table) Oxide layer thickness

[0071] - Peel strength - From the prepared clad plate test pieces, No. 3 test pieces for bending tests were cut out with the rolling direction as the longitudinal direction, and these were subjected to heat treatment at 500°C for 1 hour. The peel strength of the heat-treated plate was investigated by a bending test. The bending test was carried out using the push-bending method in accordance with JIS Z 2248:2006. The inner radius was 4 mm, the support radius was 10 mm, the distance between supports was 14 mm, and the bending angle was 60°. If partial or complete peeling occurred at the metal layer interface after the bending test, it was rated as a failure (NO), and if no peeling occurred, it was rated as a pass (YES).

[0072] Table 1 shows the test conditions, properties and peel strength test results of each of the clad plate test pieces.

[0073] [Table 1]

[0074] The above results show that the clad plate of the present disclosure does not experience peeling at the metal layer interface even in bending tests after heat treatment at 500°C, and that the peel strength is unlikely to decrease even when repeatedly exposed to high temperatures. On the other hand, the clad plate of Comparative Example 9 was subjected to a long heat treatment time, and instead of an oxide layer, a highly brittle Fe-Al intermetallic compound was formed at the interface, and peeling occurred at the metal layer interface even in a bending test after heat treatment at 500°C. The clad plates of Comparative Examples 10 and 16-20 had short bright annealing times and small oxide layer proportions, which resulted in peeling at the metal layer interface in the bending test after heat treatment at 500°C. The clad plate of Comparative Example 21 had long bright annealing times and small oxide layer proportions, which resulted in peeling at the metal layer interface in the bending test after heat treatment at 500°C. The clad plate of Comparative Example 22 had short bright annealing times and small oxide layer proportions, which resulted in peeling at the metal layer interface in the bending test after heat treatment at 500°C.

[0075] The symbols are explained as follows: 1. Clad plate 2 1st layer 3 2nd layer 4 3rd layer

[0076] The disclosure of Japanese Patent Application No. 2022-061090 is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. a first layer made of stainless steel; a second layer bonded to the first layer and made of pure aluminum or an aluminum alloy; a first oxide layer present between the first layer and the second layer and in direct contact with the first layer and the second layer; and a proportion of the first oxide layer present at the interface between the first layer and the second layer is 95.0% or more; The clad plate has a thickness of the first oxide layer of 31 nm or more and 200 nm or less.

2. a third layer made of stainless steel and joined to the second layer on the opposite side to the first layer; a second oxide layer present between the second and third layers; and and 2. The clad plate according to claim 1, wherein the proportion of the second oxide layer present at the interface between the second layer and the third layer is 95.0% or more.

3. 3. The clad plate according to claim 1, wherein the stainless steel is a martensitic stainless steel.

4. The clad plate according to claim 1 or claim 2, having a total thickness of more than 0.1 mm.

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