Surface-treated steel foil and method for manufacturing the same

Abstract

To provide surface treated steel foil with high yield strength and fatigue strength.SOLUTION: The surface treated steel foil comprises a steel sheet and an iron-nickel alloy layer formed at least on one surface of the steel sheet, in which the [001] pole density in the inverse pole figure in the rolling direction on the outermost surface of the steel foil with the iron-nickel alloy layer, is greater than the [111] pole density, and the [001] pole density in the inverse pole figure in the rolling direction on the outermost surface of the steel foil with the iron-nickel alloy layer is greater than the [101] pole density.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to surface-treated steel foil and a method for manufacturing the same. [Background technology]

[0002] Nickel-plated steel sheets are used in applications where properties such as heat resistance, electrolyte resistance, corrosion resistance, strength, and workability are required. For example, nickel-metal hydride batteries, nickel-cadmium batteries, and lithium-ion batteries are known as secondary batteries used in mobile phones, notebook PCs, and automotive applications. In these secondary batteries, nickel-plated surface-treated steel foil is used as the material for the case, current collector, etc.

[0003] For example, Patent Document 1 below discloses nickel-plated steel foil used as a material for secondary battery cases and current collectors. These documents aim to provide nickel-plated steel foil that satisfies issues such as strength, light weight, and excellent resistance to metal leaching during over-discharge. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6140611 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Nickel-plated steel foil is generally known as a corrosion-resistant material, but in recent years, with the demand for high-performance materials, even higher corrosion resistance is required for nickel-plated steel foil. At the same time, higher fatigue strength and workability are also required, and nickel-plated steel foil possessing all of these properties has not been achievable with the technologies disclosed in the aforementioned publicly available documents.

[0006] The present invention has been made in view of solving such problems, and an object thereof is to provide a surface-treated steel foil having higher corrosion resistance. Still further, another object is to provide a surface-treated steel foil having both higher fatigue strength and workability at the same time.

Means for Solving the Problems

[0007] In order to solve the problems exemplified above, a surface-treated steel foil in an embodiment of the present invention is a surface-treated steel foil having (1) a steel sheet and an iron-nickel alloy layer formed on at least one surface of the steel sheet, wherein iron-nickel alloy or nickel is present on the outermost surface of the surface-treated steel foil on the side having the iron-nickel alloy layer, and the <001> pole density in the inverse pole figure in the rolling direction on the outermost surface of the surface-treated steel foil on the side having the iron-nickel alloy layer is greater than the <111> pole density, and the <001> pole density in the inverse pole figure in the rolling direction on the outermost surface of the surface-treated steel foil on the side having the iron-nickel alloy layer is greater than the <001> pole density.

[0008] Further, the surface-treated steel foil in the above (1) preferably has (2) the <111> pole density in the inverse pole figure in the rolling direction of less than 3.0.

[0009] The surface-treated steel foil in the above (1) or (2) preferably has (3) the crystallite diameter of the nickel (220) plane or the (220) plane of the iron-nickel alloy on the surface having the iron-nickel alloy layer of 45 nm or less.

[0010] The surface-treated steel foil in the above (1) or (2) preferably has (4) the <001> pole density in the inverse pole figure in the rolling direction on the outermost surface of the surface having the iron-nickel alloy layer of 1.3 or more.

[0011] The surface-treated steel foil in the above (1) or (2) preferably has (5) the number of non-metallic inclusions having a size of φ50 μm or more contained therein of 50 pieces / thousand m ,

[0009] ,

[0008] , ,

[0012] , , , , 2 , ,

[0007] , , ,

[0011] ,

[0010] , , , or less.

[0012] In the surface-treated steel foil described in (1) or (2) above, it is preferable that (6) an iron-nickel alloy layer is formed on both sides of the steel plate.

[0013] The surface-treated steel foil in (1) or (2) above preferably has a tensile strength of 400 MPa or more and 550 MPa or less.

[0014] The surface-treated steel foil in (1) or (2) above preferably has a yield strength of 360 MPa or more.

[0015] The surface-treated steel foil in (1) or (2) above preferably has an elongation rate of 3% or more.

[0016] The surface-treated steel foil in (1) or (2) above has a nickel deposition amount of 1.5 g / m² on the surface having the iron-nickel alloy layer. 2 ~30.0g / m 2 It is preferable that this be the case.

[0017] The surface-treated steel foil in (1) or (2) above preferably has a thickness of less than 100 μm.

[0018] To solve the problems illustrated above, the method for manufacturing surface-treated steel foil according to one embodiment of the present invention is to (12) apply a coating of 1.5 g / m² to at least one side of the substrate. 2 ~70.0g / m 2 The process is characterized by comprising: a nickel plating step to form a nickel plating layer to obtain a nickel-plated material; a first heat treatment step to heat-treat the nickel-plated material to form an iron-nickel alloy; a first rolling step to roll the nickel-plated material having the iron-nickel alloy; and a second heat treatment step to heat-treat the nickel-plated material after the first rolling step under heating conditions of 500°C to 650°C for 4 to 80 hours. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide surface-treated steel foil with higher corrosion resistance. [Brief explanation of the drawing]

[0020] [Figure 1] This figure schematically shows a surface-treated steel foil according to an embodiment of the present invention. [Figure 2] This figure schematically shows a surface-treated steel foil according to another embodiment of the present invention. [Figure 3] This figure schematically shows a surface-treated steel foil according to another embodiment of the present invention. [Figure 4] This is a flowchart illustrating a method for manufacturing surface-treated steel foil according to an embodiment of the present invention. [Figure 5] This flowchart shows a method for manufacturing surface-treated steel foil according to another embodiment of the present invention. [Figure 6A] This figure shows an example of an inverse pole diagram of an embodiment of the present invention calculated by the EBSD method, specifically an inverse pole diagram in the rolling direction on the surface having an iron-nickel alloy layer on the surface of Example 1. The rolling direction is also indicated as RD. [Figure 6B] This figure shows a method for determining the extreme density of a surface according to an embodiment of the present invention. [Modes for carrying out the invention]

[0021] ≪Surface-treated steel foil 10≫ The following describes embodiments for implementing the surface-treated steel foil of the present invention. Figure 1 is a schematic diagram showing one embodiment of the surface-treated steel foil 10 of the present invention.

[0022] The surface-treated steel foil 10 of this embodiment has a base material 20 and an iron-nickel alloy layer 30. Although the surface-treated steel foil 10 shown in Figure 1 has an iron-nickel alloy layer 30 on one side, it is not limited to this, and the base material 20 may have iron-nickel alloy layers 30 on both sides, as shown in Figure 2. Furthermore, the iron-nickel alloy layer 30 may be placed on the outermost surface of the surface-treated steel foil 10 as shown in Figure 1, or, although not shown, another metal layer may be formed on the side of the iron-nickel alloy layer 30 opposite to the base material 20.

[0023] <Base material 20> In this embodiment, a rolled steel sheet is used as the base material 20 for the surface-treated steel foil 10. Specifically, suitable types include low-carbon steel (carbon content 0.01 to 0.15 wt%), such as low-carbon aluminum-killed steel, ultra-low-carbon steel with a carbon content of less than 0.01 wt%, or non-aging ultra-low-carbon steel obtained by adding Ti, Nb, etc. to ultra-low-carbon steel.

[0024] The thickness of the substrate 20 used in the surface-treated steel foil 10 of this embodiment is preferably in the range of 10 μm to less than 100 μm. When used as a current collector for a battery, where volume and gravimetric energy density are important, the thickness is more preferably 25 μm to less than 100 μm, and even more preferably 30 μm to 80 μm, from the viewpoint of strength and desired battery capacity. The thickness of the substrate 20 can be measured by cross-sectional observation with an optical microscope or a scanning electron microscope (SEM).

[0025] Here is an example of the component composition of the base material 20. The main element in the base material 20 is Fe. Other components include C: 0.0001-0.15 wt%, Si: 0.001-0.5 wt%, Mn: 0.01-1.0 wt%, P: 0.001-0.05 wt%, S: 0.0001-0.02 wt%, Al: 0.0005-0.20 wt%, N: 0.0001-0.0040 wt%, etc. In addition, Ti, Nb, B, Cu, Ni, Sn, and Cr may be included as additional components. For example, when the C content is in the range of 0.001 to 0.01% by weight, one or two types of Ti may be included in the range of 0.01 to 0.1% by weight and Nb in the range of 0.001 to 0.05% by weight. Furthermore, in this embodiment, a steel sheet with a Cr content of less than 10.5% is more preferable for the base material 20. In addition, it may contain impurities that are inevitably introduced during the manufacturing process.

[0026] In this embodiment, the substrate 20 contains 50 nonmetallic inclusions with a size of φ50 μm or larger, per thousand m². 2The following is preferable. Minute non-metallic inclusions can be detected by leakage magnetic flux testing using a micro-internal defect detector. As the micro-internal defect detector, the device (new type IDD) disclosed in "Toyo Kohan Vol. 33, pages 17-22" can be used.

[0027] <Iron-nickel alloy layer 30> The iron-nickel alloy layer 30 contained in the surface-treated steel foil 10 of this embodiment is an alloy layer containing iron (Fe) and nickel (Ni), and is an alloy layer containing an alloy made of iron and nickel (also referred to as "iron-nickel alloy" or "Fe-Ni alloy"). The state of this iron-nickel alloy may be a solid solution, eutectoid / eutectic, or compound (intermetallic compound), or these may coexist.

[0028] The iron-nickel alloy layer 30 contained in the surface-treated steel foil 10 of this embodiment may contain other metallic elements and unavoidable impurities, as long as they can solve the problems of the present invention, but it is necessary that the amount does not interfere with the crystal lattice of Ni or FeNi. For example, the iron-nickel alloy layer 30 may contain metallic elements such as cobalt (Co) and molybdenum (Mo), or additive elements such as boron (B). The proportion of metallic elements other than iron (Fe) and nickel (Ni) in the iron-nickel alloy layer 30 is preferably 5% by weight or less, and more preferably 1% by weight or less. Since the iron-nickel alloy layer 30 may be a binary alloy composed substantially only of iron and nickel, the lower limit of the content of other metallic elements excluding unavoidable impurities is 0% by weight. The types and amounts of other metallic elements present can be measured by known means such as X-ray fluorescence (XRF) spectroscopy, glow discharge surface spectroscopy (GDS), or Auger electron spectroscopy (AES).

[0029] The iron-nickel alloy layer 30 contained in the surface-treated steel foil 10 of this embodiment is formed through the following steps: forming a nickel plating layer on a base plate to create a nickel-plated material (nickel plating step), applying heat treatment to the nickel-plated material (first heat treatment step), rolling the nickel-plated material after heat treatment (first rolling step), and applying a second heat treatment (second heat treatment step), in this order. Furthermore, the rolling process in the "first rolling process" described above will also be referred to as "re-rolling" to distinguish it from the rolling of the base material (cold rolling from a hot coil). Furthermore, the heat treatment in the "second heat treatment process" described above will also be simply referred to as the "second heat treatment." After the second heat treatment process, a rolling process (second rolling process) may be carried out to the extent that it does not deviate from the constituent range of the extreme density relationship described later. However, the manufacturing method of the surface-treated steel foil 10 in this embodiment is not limited to the manufacturing method described above.

[0030] Nickel plating methods include, for example, electrolytic plating, electroless plating, hot-dip plating, and dry plating. Of these, electrolytic plating is particularly preferred from the viewpoint of cost and film thickness control. The manufacturing method of the surface-treated steel foil of this embodiment will be described in detail later.

[0031] (extreme density) In this embodiment, the surface-treated steel foil 10, in the inverse pole figure in the rolling direction on the surface having an iron-nickel alloy layer, <001> Extreme density and <111> The relationship with the polar density satisfies certain conditions, and <001> Extreme density and <101> It is characterized by satisfying certain conditions in relation to extreme density. That is, the inverse pole figure in the rolling direction on a surface having an iron-nickel alloy layer <001> Extreme density <111> Greater than the extreme density, and <001> Extreme density <101> It is characterized by having a density greater than that of the polarity. By satisfying both of these conditions, corrosion resistance can be improved. In this specification, the inverse pole figure in the rolling direction may be simply referred to as the inverse pole figure.

[0032] In this embodiment, however, it is not limited to the following, <001> The extreme density is preferably 1.3 or higher, more preferably 2.1 or higher, and even more preferably 2.2 or higher. The upper limit is not particularly limited, but is usually 6.0 or lower, and preferably 5.0 or lower. On the other hand, in this embodiment, <111> The extreme density is preferably less than 3.0, and more preferably less than 2.0. <101> The polar density is typically between 0.1 and 2.0.

[0033] The relationship between corrosion resistance and polar density will be explained below. In a typical nickel-plated steel sheet, the inverse pole figure of the nickel-plated surface in the RD direction of the steel sheet is <101> Extreme density is high and often becomes the preferred orientation. On the other hand, after rolling or tensile processing, in the RD direction, <111> Extreme density is often high and this orientation is the preferred orientation. This is because it is a morphology resulting from slip deformation occurring at the slip plane {111}, causing the crystal to rotate. Therefore, it can be easily inferred that when such a preferred orientation is present, the crystal contains a large amount of strain.

[0034] In the surface-treated steel foil of this embodiment obtained by the manufacturing method described later, the amount of nickel plating, the conditions of the first heat treatment, the nickel plating layer after the first rolling and second heat treatment, or the nickel plating layer after the above process and the second rolling, will exhibit a preferred orientation as a result of being complexly affected by processing distortion, recovery, recrystallization, etc. The rolling direction of this embodiment <001> A state of extremely high density means that the lattice distortion, which can be the starting point of corrosion, is relatively reduced, thus resulting in superior corrosion resistance. Furthermore, this state also means that there is a large tolerance for further processing deformation, making it highly likely that the material can be processed into complex shapes. In this way, it is thought that it is possible to balance corrosion resistance, yield strength, and elongation at a high level. However, the mechanism behind this is not necessarily fully understood.

[0035] In this embodiment, the "inverse pole figure in the rolling direction on the surface having the iron-nickel alloy layer" refers to the result of measuring the inverse pole figure in the rolling direction (RD direction) in crystal orientation analysis using EBSD (Electron Back Scatter Diffraction) on the side of the surface-treated steel foil 10 where the iron-nickel alloy layer 30 is provided. In this case, the crystal orientation analysis is performed using known analysis software (for example, OIM Analysis from TSL Solutions). Note that a higher pole density indicates a higher orientation of that direction.

[0036] (crystallite size) Furthermore, in this embodiment, it is preferable that the crystallite size of the nickel(220) plane or the (220) plane of the iron-nickel alloy on the surface having the iron-nickel alloy layer is 45 nm (450 Å) or less. A crystallite refers to the largest aggregate of microcrystals that can be considered as a single crystal. In this embodiment, it was found that when the crystallite size is 45 nm or less, it is possible to impart high fatigue strength to the resulting surface-treated steel foil. That is, in this embodiment, since the crystallite size of the nickel(220) plane or the (220) plane of the iron-nickel alloy on the surface having the iron-nickel alloy layer is 45 nm or less, the yield strength is increased, and an improvement in fatigue strength can be achieved. Furthermore, as a by-effect of the above characteristics, it is possible to suppress the yield elongation, making it possible to realize a material with superior processability. While there are no specific restrictions on the lower limit of the crystallite size, it is preferable that it be 5 nm or larger, as a size that is too small may result in the nickel film becoming too hard.

[0037] In the surface-treated steel foil 10 of this embodiment, the crystallite size on the surface having the iron-nickel alloy layer is determined from the peak full width at half maximum by X-ray diffraction using the following formula. X-ray diffraction is measured, for example, using a known X-ray diffractometer. The crystallite size is calculated using the peak of the (220) plane of the iron-nickel alloy that appears at 2θ = 72 to 79°. D = K × λ / (β × cosθ) D: Crystallite size K: Scherrer constant (using K = 0.94) λ: Wavelength of the X-ray used β: Half-value width of the diffracted X-ray of the crystallite θ: Bragg angle

[0038] (Thickness of the surface-treated steel foil 10)[[ID=;12]] Next, the thickness of the entire surface-treated steel foil 10 in the present embodiment will be described. In the present embodiment, the overall thickness of the surface-treated steel foil 10 is preferably less than 100 μm. Further, from the viewpoints of strength and the desired battery capacity, etc., it is more preferably 10 μm or more and less than 100 μm, still more preferably 25 μm or more and less than 100 μm, and particularly preferably 30 μm or more and 80 μm or less.

[0039] Note that for the "thickness of the surface-treated steel foil 10" in the present embodiment, thickness measurement with a micrometer is preferred.

[0040] (Nickel deposition amount) In the surface-treated steel foil 10 of the present embodiment, the deposition amount of nickel on the surface having the iron-nickel alloy layer 30 is 1.5 g / m 2 ~30.0 g / m 2 which is preferable from the viewpoints of yield point strength and fatigue strength. From the same viewpoints, the lower limit value of the nickel deposition amount is more preferably 3.0 g / m 2 and still more preferably 5.0 g / m<00?00010>and particularly preferably 10.0 g / m 2 The upper limit value of the nickel deposition amount is more preferably 25.0 g / m 2 and still more preferably 20.0 g / m<00000?3>and particularly preferably 17.5 g / m 2 This is particularly preferable.

[0041] Also, in the surface-treated steel foil 10 of the present embodiment, the iron-nickel alloy layer 30 may be formed on both sides of the base material 20 as shown in FIG. 2. In that case, the total deposition amount of nickel on both surface sides is 3.0 to 60.0 g / m 2It is preferable that this be the case. The amount of nickel deposited as described above can be determined by measuring the total amount of nickel in the iron-nickel alloy layer 30 using an X-ray fluorescence apparatus. However, this method is not limited to this method, and other known measurement methods can also be used.

[0042] In this embodiment, the iron-nickel alloy layer 30 may be a layer without a brightener added, or it may be a layer formed by adding a brightener (including a brightener for semi-gloss finishes). It should be noted that the terms "glossy" and "matte" used above are based on visual evaluation of the appearance, and it is difficult to distinguish them precisely using numerical values. Furthermore, the degree of gloss may change depending on other parameters such as the bath temperature, which will be discussed later. Therefore, the terms "glossy" and "matte" used in this embodiment are defined solely in terms of the presence or absence of a glossing agent.

[0043] (Tensile strength) The tensile strength of the surface-treated steel foil 10 in this embodiment may be between 300 MPa and 750 MPa, but from the viewpoint of a more favorable yield strength and brittleness, it is preferable to have a tensile strength between 350 MPa and 590 MPa, and particularly preferable to have a tensile strength between 400 MPa and 550 MPa. In this embodiment, the tensile strength of the surface-treated steel foil 10 can be measured, for example, as follows: A metal piece of type 5 according to JIS Z 2241 is punched out. Then, a tensile test can be performed on this test piece in accordance with the tensile test method conforming to JIS Z 2241.

[0044] (yield point strength) In the surface-treated steel foil 10 of this embodiment, the yield strength may be between 200 MPa and 720 MPa, but from the viewpoint of subsequent processability, a yield strength of 360 MPa or higher is preferable. Furthermore, from the viewpoint of brittleness, a yield strength of 550 MPa or lower is preferable. The yield strength can be measured, for example, using the same apparatus as the tensile strength described above.

[0045] (Growth rate) The elongation of the surface-treated steel foil 10 in this embodiment is considered to be between 1% and 35%, but from the viewpoint of more favorable yield strength and fatigue strength, it is particularly preferable that the lower limit of the elongation be 3% or more. While an elongation of 35% or less is acceptable, a yield elongation of 0.5% or less is preferable for suppressing stretcher strain during sheet feeding and processing. The lower limit of the yield elongation is 0. In this embodiment, the elongation of the surface-treated steel foil 10 refers to the value measured in accordance with JIS Z2241 (Methods for Tensile Testing of Metallic Materials).

[0046] The surface-treated steel foil 10 of this embodiment has 50 minute non-metallic inclusions per thousand m². 2 The following is preferable. Minute non-metallic inclusions can be detected by leakage magnetic flux testing using a micro-internal defect detector. As the micro-internal defect detector, the device (new type IDD) disclosed in "Toyo Kohan Vol. 33, pages 17-22" can be used.

[0047] As shown in Figure 3, the surface-treated steel foil 10 in this embodiment may further have a metal layer 40 formed on the iron-nickel alloy layer 30. Examples of metal materials constituting the metal layer 40 include nickel, chromium, titanium, copper, cobalt, iron, etc. Of these, nickel or nickel alloys are particularly preferred due to their excellent corrosion resistance and strength.

[0048] Furthermore, in the surface-treated steel foil 10 of this embodiment, a roughened nickel layer 50 may be formed on the outermost surface, although this is not shown in the figures. Note that the above-mentioned metal layer 40 may be a roughened nickel layer, or a roughened nickel layer may be formed on the above-mentioned metal layer 40. Details regarding the roughened nickel layer are omitted here, as they are described in, for example, our own application (WO2021 / 020338, etc.).

[0049] ≪Method for manufacturing surface-treated steel foil≫ An example of a manufacturing method for the surface-treated steel foil 10 of this embodiment will be explained with reference to the figures.

[0050] As an example of the manufacturing method of this embodiment, as shown in Figure 4, the process involves forming a nickel plating layer on a base plate to create a nickel-plated material (STEP A: Nickel Plating Process), and then subjecting the nickel-plated material to heat treatment (STEP B: First Heat Treatment Process). The process involves rolling the nickel-plated material after heat treatment (STEP C: First Rolling Process), followed by a second heat treatment (STEP D: Second Heat Treatment Process), in that order.

[0051] In the surface-treated steel foil obtained by the manufacturing method of this embodiment, iron from the base material 20 (original plate) is diffused into the nickel plating layer to form an iron-nickel alloy layer 30, and the inverse pole figure in the rolling direction on the surface having the iron-nickel alloy layer 30 <001> Extreme density <111> The density is greater than the polar density, and the inverse pole figure in the rolling direction on the surface having the iron-nickel alloy layer <001> Extreme density <101> This becomes greater than the polar density (hereinafter also referred to as the "relationship with polar densities").

[0052] Alternatively, you may repeat STEP C and STEP D after STEP D. Furthermore, the rolling process described in the "First Rolling Process" above will also be referred to as "re-rolling" to distinguish it from the rolling of the original sheet. Furthermore, the heat treatment in the "second heat treatment process" described above will also be simply referred to as the "second heat treatment."

[0053] Furthermore, as shown in Figure 5, a second rolling step (STEP E) may be added sequentially for purposes such as further thickness adjustment or tempering. It is preferable that the above-mentioned relationship of extreme density is still satisfied even after going through this second rolling step. After STEP D or STEP E, there may be steps such as a re-plating step or a roughened nickel layer formation step, although these are not shown in the diagram. The following provides a detailed explanation of each step.

[0054] <Pre - process> First, prepare a steel sheet to be the base plate. The base plate mentioned here refers to the steel plate before rolling as follows, which becomes the base material part when it becomes a surface - treated steel foil through each process described later. Therefore, similar to the base material, the steel plate to be the base plate is preferably low - carbon steel or extra - low - carbon steel. Also, the base plate is preferably a cold - rolled steel plate. Regarding the component composition of the steel plate to be the base plate, particularly, the sulfur (S) content being 0.0001 wt% to 0.02 wt% is preferable from the viewpoint of the corrosion resistance of the nickel film of the obtained surface - treated steel foil. The upper limit of the S content is more preferably 0.018 wt%, and even more preferably 0.015 wt%.

[0055] The thickness of the base plate is not particularly limited, but in order to obtain a thickness such that it is called a steel foil after the first rolling process described later, the base plate is preferably 150 - 500 μm. In order to obtain a foil with a thickness of 120 μm or less after the first rolling process described later, it is more preferable that the thickness of the base plate is 400 μm or less. This is because a thinner base plate relaxes the rolling reduction during rolling and is more likely to prevent the exposure of iron. In order to obtain a foil with a thickness of less than 100 μm after the first rolling process described later, it is even more preferably that the thickness of the base plate is 350 μm or less, and particularly preferably 300 μm or less. When a cold - rolled steel plate is used as the base plate, generally, the "annealing" performed to remove the work hardening of the cold - rolled steel plate can be carried out before the nickel plating process described later. Also, in this embodiment, it is possible to omit the "annealing" of this cold - rolled steel plate. This is because in the first heat - treatment process mainly aimed at softening the nickel plating described later, the work hardening of the cold - rolled steel plate can be removed simultaneously.

[0056] <STEP A: Nickel plating process> The nickel plating process is a step of applying nickel, which is necessary to form the iron-nickel alloy layer 30 to be formed in the second heat treatment described later, to at least one side of the original sheet as a nickel plating layer. In this nickel plating process, the amount of nickel plating applied to the base plate is 1.5 g / m² per side. 2 ~70.0g / m 2 Preferably, 10 g / m² per side on both sides. 2 More than ~70g / m 2 The following nickel plating is applied, and at least one side is 5g / m² per side. 2 It is even more preferable to use 10 g / m² or more. 2 It is particularly preferable to use the above amount. The upper limit is 70g / m². 2 The following is more preferable: 65 g / m 2 The following are even more preferable.

[0057] Nickel plating thickness: 70 g / m² 2 If the value exceeds this, productivity will be poor, and even after the first heat treatment process, the foil may break during the first rolling process due to insufficient elongation of the entire foil. On the other hand, the amount of nickel plating deposited is 5 g / m². 2 If the value is less than the required amount, the iron-nickel alloy layer 30 obtained after the second heat treatment process may be deficient in nickel, failing to satisfy the extreme density relationship or resulting in unfavorable yield strength and fatigue strength.

[0058] In the nickel plating process described above, known conditions can be applied to the electroplating conditions. Examples of plating conditions are shown below.

[0059] [Example of nickel plating bath and plating conditions] • Bath composition: Known watt bath Nickel sulfate hexahydrate: 200~300g / L Nickel chloride hexahydrate: 20-60 g / L Boric acid: 10-50 g / L Bath temperature: 40~70℃ pH: 3.0~5.0 Stirring: Air stirring or jet stirring Current density: 5 - 30 A / dm 2 Regarding the bath composition, in addition to the above-mentioned Watts bath, known nickel sulfamate baths or citrate baths may also be used. Furthermore, additives such as known brighteners may be added to the plating bath to obtain bright nickel plating or semi-bright nickel plating.

[0060] <STEP B: First heat treatment process> Next, the first heat treatment process will be described. The first heat treatment process is the heat treatment process that is first carried out after the above-mentioned nickel plating process and is carried out in a reducing atmosphere. The main purpose of this first heat treatment process is to soften the nickel plating layer formed in the above-mentioned nickel plating process prior to the rolling process described later.

[0061] ​​​​​​​​​As an example of the temperature and time for continuous annealing, it is preferable to perform the process at a temperature of 600°C to 950°C with a soaking time of 15 to 150 seconds. Lower temperatures or shorter times than this may result in insufficient softening, which is undesirable as it may make it difficult to form the foil during the subsequent first rolling process. On the other hand, higher temperatures or longer times than the above heat treatment range are undesirable from a cost perspective, as they may lead to significant changes in the mechanical properties of the base material, such as the steel foil, resulting in a substantial decrease in strength. Furthermore, a soaking time of 20 to 150 seconds is more preferable for sufficient softening.

[0064] As an example of temperature and time for batch annealing (box annealing), it is preferable to perform the process at a temperature of 450°C to 690°C, with a soaking time of 1.5 to 20 hours, and a total time of 4 to 80 hours including heating, soaking, and cooling. Lower temperatures or shorter times are undesirable because the softening will be insufficient, making it difficult to form the foil during the subsequent first rolling process. On the other hand, higher temperatures or longer times than the above heat treatment range are undesirable because they may cause significant changes in the mechanical properties of the base material, such as the steel foil, potentially leading to a substantial decrease in strength, or from a cost perspective.

[0065] However, the amount of nickel plating is 10 g / m² per side. 2 The following applies especially to one side: 6g / m 2 In the following cases of low levels, high-temperature or long-duration heat treatment may lead to increased diffusion of Fe from the iron of the base material during the second heat treatment, potentially reducing corrosion resistance. Therefore, continuous annealing at a temperature of less than 780°C is preferred, and more preferably less than 750°C.

[0066] Note that when the first heat treatment step is completed, the nickel in the iron of the base plate and the nickel plating layer diffuses with each other due to heat, forming an iron-nickel diffusion layer. That is, the surface where nickel plating was performed in the above nickel plating step forms an iron-nickel diffusion layer, or an iron-nickel diffusion layer and a soft nickel layer, when the first heat treatment step is completed. In other words, in this embodiment, the iron-nickel diffusion layer refers to an alloy layer obtained by heat treatment of iron and nickel that does not satisfy the above-mentioned characteristic of the pole density relationship. Also, in this embodiment, the soft nickel layer refers to a layer of softened nickel in which the iron of the base plate has not diffused into the nickel of the nickel plating layer by heat treatment.

[0067] Note that in this embodiment, the above-mentioned relationship of the pole density only needs to be satisfied when the second heat treatment step described later is completed. Therefore, when the first heat treatment step is completed, the above-mentioned relationship of the pole density may or may not be satisfied.

[0068] [[ID=�]] Note that the thickness of the steel plate after heat treatment after the first heat treatment step is the same as the thickness of the nickel-plated steel plate after the nickel plating step.

[0069] <STEP C: First Rolling Step> Next, the first rolling step in the manufacturing method of this embodiment will be described. The first rolling step in this embodiment is a step of rolling the nickel-plated material after heat treatment after the above nickel plating step and the first heat treatment step. The purpose of this first rolling step is to obtain a desired foil thickness, or to obtain a thickness that is not problematic in advance in order to obtain a foil of a desired thickness when the second rolling step described later is completed.

[0070] The rolling reduction rate in this first rolling step is preferably 35% or more. By setting it to 35% or more, it becomes possible to obtain a surface-treated steel foil having a preferable yield point strength and fatigue strength. The rolling reduction rate is more preferably 50% or more. However, as the reduction ratio increases, the lattice strain increases and the relationship with extreme density is no longer satisfied. Therefore, it is preferable that the reduction ratio be 85% or less, more preferably 80% or less, even more preferably 78% or less, and particularly preferably 75% or less.

[0071] In this first rolling process, there may be one set of rolling rolls or multiple sets. A typical rolling mill consists of multiple sets of upper and lower rolls, i.e., rolling rolls, that directly act to thin the sheet, and rolls for passing the sheet through. During rolling, there may be one set of rolling rolls acting on the rolling process, or multiple sets of rolling rolls may be acting. In this embodiment, there may be one set or multiple sets of rolling rolls acting in the first rolling process, and for example, three sets of rolling rolls may be used to pass the sheet through twice, resulting in a total of six sets of rolling rolls for rolling. Generally, as the number of times the sheet passes through the rolling rolls increases, problems due to work hardening are more likely to occur during rolling. Therefore, it is preferable to have six sets or fewer rolling rolls acting on the rolling process, and more preferably four sets or fewer. Here, one set of rolling rolls refers to the upper and lower rolls that directly touch the sheet and whose thickness changes before and after passing through them.

[0072] Furthermore, the reduction ratio mentioned above refers to the reduction ratio obtained from the thickness before and after the first rolling process. In other words, when the sheet metal is passed through three sets of rolling rolls twice, it refers to the reduction ratio obtained from the thickness before the first pass and the thickness after the second pass.

[0073] In the first rolling process, the reduction ratio by the first set of rolling rolls is not particularly limited, but it is preferable to set it to 35% or more from the viewpoint that thinning the material in its initial, softest state makes it easier to suppress the exposure of iron. However, since the first set has the thickest thickness before rolling, it is preferable to set it to less than 50% from the viewpoint that if the reduction amount is too large, it becomes difficult to control the uniformity of the thickness.

[0074] Note that the nickel adhesion amount on the steel foil after the first rolling process, that is, the amount of nickel per unit area after the nickel plated by the nickel plating process is stretched by rolling, is preferably at least 1.2 g / m 2 on at least one side from the viewpoint of corrosion resistance, more preferably 6.0 g / m 2 or more, and still more preferably 6.5 g / m 2 or more. Also, in order to obtain more stable corrosion resistance, it is preferable that both sides of the steel foil are each more than 1.2 g / m 2 .

[0075] <STEP D: Second heat treatment process> Next, the second heat treatment process in the manufacturing method of the present embodiment will be described. The second heat treatment process is a process of annealing the material after the first rolling process in a reducing atmosphere. This second heat treatment process is performed for the purpose of making the <001> pole density in the rolling direction on the surface having the iron-nickel alloy layer larger than the <111> pole density and making the <001> pole density in the rolling direction on the surface having the iron-nickel alloy layer larger than the <101> pole density.

[0076] More specifically, first, the iron-nickel diffusion layer or the iron-nickel diffusion layer and the soft nickel layer formed on the surface by the first heat treatment described above are rolled together with the original plate in the first rolling process. This rolling reduces the thickness of the material. At the same time, it is considered that the <111> orientation becomes parallel to the rolling direction, that is, the <111> pole density increases.

[0077] Then, in the second heat treatment process, the lattice strain is eliminated (removed) at the locations where the thickness has become extremely thin or strain has been introduced by the first rolling process, and the relationship of the pole density is satisfied. Thereby, a surface-treated steel foil having both yield point strength and elongation is obtained.

[0078] The heat treatment conditions in the second heat treatment process vary depending on the state of the steel foil before the second heat treatment in order to satisfy the relationship of the pole density. For example, if the second heat treatment process is continuous annealing, it is carried out at a temperature of 680°C to 950°C with a soaking time of 30 to 150 seconds. On the other hand, in the case of batch annealing (box annealing), it is carried out at a temperature of 500°C to 650°C with a soaking time of 1.5 to 20 hours, and the total time including heating, soaking, and cooling is in the range of 4 to 80 hours. In this embodiment, the second heat treatment step may be box annealing or continuous annealing. However, box annealing offers advantages such as ease of handling, the ability to control mechanical properties with greater precision, the ability to further suppress age hardening and stretcher strain, and the ease of obtaining the desired extreme density across the entire surface, even with wide steel foils.

[0079] If the heat treatment temperature is lower or the time is shorter than the above, <001> This is undesirable because it may prevent the extreme density from becoming sufficiently high.

[0080] Furthermore, there are no restrictions as long as the configuration satisfies the relationship of extreme density, but especially when the reduction ratio in the first rolling process is 50% or more, this second heat treatment process is sufficient. <001> To increase the extreme density and eliminate lattice distortion, continuous annealing is preferably performed at 700°C to 750°C with a soaking time of 60 to 150 seconds or at 760°C or higher, while box annealing is preferably performed at 500°C or higher but less than 540°C with a soaking time of 4 hours or higher or at 540°C or higher.

[0081] Furthermore, the amount of nickel deposited on the surface-treated steel foil obtained after the second heat treatment process is the same as the amount of nickel deposited after the first rolling process described above.

[0082] In particular, in the case of continuous steel strips, a surface treatment to prevent adhesion of nickel plating may be applied before the second heat treatment process. Examples of this surface treatment to prevent adhesion of nickel plating include the formation of a silicon oxide layer in a bath mainly composed of sodium orthosilicate, as disclosed in Japanese Patent Application Publication No. 08-333689. This surface treatment to prevent adhesion of nickel plating may be removed after the second heat treatment process.

[0083] <STEP E: Second rolling process> Next, the second rolling process after the second heat treatment process will be described. This second rolling process is a process for further adjusting the thickness and tempering of the surface-treated steel foil. Note that this second rolling process is not an essential process and can be omitted as appropriate.

[0084] In this second rolling process, the rolling reduction (the rolling reduction calculated from the difference in thickness before and after the second rolling process) is preferably less than 35%, more preferably 33% or less, and even more preferably 25% or less. There is no particular lower limit, and it is 0% or more including temper rolling where the actual thickness does not change.

[0085] Note that at the time when this second rolling process is completed, it is necessary to satisfy the above-mentioned relationship of the magnetic density.

[0086] Also, since the nickel deposition amount decreases according to the rolling reduction of the second rolling process, when passing through the second rolling process, it is necessary to set the nickel deposition amount to a preferable amount after the second rolling. The preferable nickel deposition amount after the second rolling is preferably more than 1.2 g / m on at least one side from the viewpoint of corrosion resistance, more preferably 6.0 g / m 2 or more, and even more preferably 6.5 g / m 2 or more. Also, in order to obtain more stable corrosion resistance, it is preferable that both sides of the steel foil are each more than 5.0 g / m 2 or more. 2

[0087] <Other processes> Note that although not shown in the figure, a process (re-plating process) of forming a metal layer 40 by plating may be provided after at least any one of the first rolling process, the second heat treatment process, and the second rolling process. Alternatively, in the method for manufacturing the surface-treated steel foil 10 of the present embodiment, a process of forming a roughened nickel layer 50 on the outermost surface may be included.

[0088] ​In this embodiment, the manufacturing method for the surface-treated steel foil 10 can be a continuous manufacturing method (for example, a roll-to-roll method), or it can be a batch manufacturing method using cut plates, for example.

[0089] From the viewpoint of yield strength and fatigue strength, it is preferable that the surface-treated steel foil obtained by the manufacturing method of this embodiment satisfies at least one of the following conditions: tensile strength of 400 MPa or more and 550 MPa or less, yield strength of 360 MPa or more, and elongation of 3% or more. Furthermore, the surface-treated steel foil obtained by the manufacturing method of this embodiment has a Ni adhesion amount of 1.2 g / m² on the surface having an iron-nickel alloy layer. 2 ~30.0g / m 2 This is preferable from the viewpoint of corrosion resistance.

[0090] Examples The present invention will be described in more detail below with reference to examples. First, the measurement method used in the examples will be described.

[0091] [Acquisition of extreme density using EBSD method] In the obtained surface-treated steel foil, the inverse pole figure in the rolling direction on the surface with the iron-nickel alloy layer was measured by performing crystal orientation analysis using EBSD (Electron Back Scattering Diffraction) measurement with a scanning electron microscope (SEM). <001> , <111> , <101> The extreme density was evaluated. A scanning electron microscope (FE-SEM, SU8020) manufactured by Hitachi High-Technologies Corporation was used, and for crystal orientation analysis by EBSD measurement, the analysis software (OIM Analysis, manufactured by TSL Solutions Corporation) was used. The measurement conditions for EBSD measurement were as follows.

[0092] (a) SEM conditions Beam conditions: Acceleration voltage 20kV, irradiation current 20μA • Working distance: 20mm • Observation field: 100 μm in the rolling direction (RD) × 120 μm in the direction perpendicular to the rolling direction (TD) • Observation surface: The surface of the sample * Mount the sample so that the measurement coordinate system and the sample coordinate system are the same. In other words, the measurement was mounted so that the RD in the measurement coordinate system coincided with the rolling direction of the sample.

[0093] (b)EBSD conditions • Measurement program: OIM Data Collection (Ver. 6.21) Step width: 0.2 μm

[0094] (c) Analysis conditions • Data analysis program: OIM Analysis (Ver. 6.20) *In the reverse pole diagram of the RD (rolling direction), <111> , <101> , <001> The extreme density was evaluated.

[0095] EBSD measurements were performed, and an inverse pole figure in the rolling direction was obtained using a data analysis program. Figure 6A shows the degree of accumulation in each direction from the inverse pole diagram, with the pole density in a state where there is no statistical bias in crystal orientation, so-called random state, set to 1, and the orientation state of the texture displayed as contour lines. From this figure, it can be seen that the degree of accumulation in the < 0 0 1 > direction is high in the RD (rolling direction) inverse pole diagram of the target sample.

[0096] In the present invention <111> , <101> , <001> The polar density of orientation was determined using contour plots in the RD (rolling direction) for each sample, as shown in Figure 6A. Specifically, as shown in Figure 6B, in the analysis software, <111> In the case of extreme density, vertex A, <101> In this case, vertex B, <001> In this case, the values ​​that can be read by selecting the position of vertex C were used as the polar density for each direction. Note that in the vicinity of each vertex (for example, within the same colored area on the contour map), the change in polar density is small, so it is also acceptable to select the vicinity of the vertex (the same colored area on the contour map) and adopt the maximum polar density that can be read.

[0097] [Method for measuring crystallite size] To measure the crystallite size, an X-ray diffractometer (manufactured by Rigaku Corporation, fully automatic multi-purpose horizontal X-ray diffractometer) was used. X-ray diffraction was performed using the SmartLab instrument. <Device configuration> ·X-ray source: CuKα • Goniometer radius: 300mm ·Optical system: Concentration method (Induction-side slit system) • Solar slit: 5° • Longitudinal limiting slit: 5mm • Divergent slit: 2 / 3° (Light-receiving slit system) • Scattering slit: 2 / 3° • Solar slit: 5° • Light-receiving slit: 0.3mm • Monochromatic method: Counter monochromator method • Detector: Scintillation counter <Measurement parameters> • Tube voltage-current: 45kV 200mA ·Scanning axis: 2θ / θ (concentration method) • Scanning mode: Continuous • Measurement range: 2θ 72~79° • Scanning speed: 2° / min Step: 0.02°

[0098] A test specimen was cut from the surface-treated steel foil and placed on a measurement sample stage. X-ray diffraction measurements were performed using the reflection method on the surface with the iron-nickel alloy layer in the range of X-ray diffraction angle 2θ = 72 to 79°. Subsequently, the crystallite size was calculated from the obtained measurement values ​​using Rigaku Corporation's integrated powder X-ray analysis software PDXL based on the following formula. Specifically, since the obtained measurement chart showed peak overlap between the iron-nickel alloy and nickel (220) planes, peak separation and calculation of the crystallite size after peak separation were performed by optimizing the peaks using the above-mentioned X-ray analysis software in the range of X-ray diffraction angle 2θ = 72 to 79°. If, after peak separation, the peak height (cps) derived from nickel was higher than the peak height (cps) derived from the iron-nickel alloy, the crystallite size of the nickel-derived peak was used as a substitute. Table 2 shows the crystallite sizes. Here, in the crystallite size value column of Table 2, _Ni or _FeNi indicates the peak used for crystallite size calculation. D = K × λ / (β × cosθ) D: Crystallite size K: Scherrer constant (using K=0.94) λ: Wavelength of the X-ray used β: Full width at half maximum of the diffracted X-ray of a crystallite θ: Bragg angle

[0099] [Neutral salt spray test and corrosion resistance evaluation] The obtained surface-treated steel foil was cut to a size of 60 mm in width and 130 mm in length. One side was designated as the evaluation surface, and the other end was masked with tape. Then, in accordance with JIS Z 2371:2015 neutral salt spray test, the foil was sprayed with a 5% salt solution (NaCl = 50 g / L) at a spray temperature of 35°C for 2 hours using a salt spray tester manufactured by Suga Test Instruments Co., Ltd. The number of rust spots on the surface with the iron-nickel alloy layer after spraying was visually counted and scored as follows for evaluation. 5 points: 150 pieces / dm 2 less than 4 points: 150~250 pieces / dm 2 less than 3 items: 250~350 pieces / dm 2 less than 2 items: 350~500 pieces / dm 2 less than 1 item: 500 pieces / dm 2 That's all.

[0100] [Evaluation of mechanical properties by tensile testing] Tensile strength (TS), upper yield strength (YP), yield elongation (YP·EL), and fracture elongation (EL) were measured using the following methods. First, metal pieces conforming to JIS Z 2241 No. 5 were punched out. Next, tensile tests were performed on these test pieces in accordance with the tensile test method compliant with JIS Z 2241. The test pieces were taken so that the tensile direction was parallel to the rolling direction. A tensile testing machine (ORIENTEC Tensilon RTC-1350A universal material testing machine) was used for the tensile test. The measurement conditions were room temperature and a tensile speed of 10 mm / min. In accordance with JIS Z 2241, tensile strength, yield point, (upper yield point), yield elongation, and elongation (break elongation) were measured.

[0101] [Measurement of minute inclusions using magnetic flux leakage testing] Minute non-metallic inclusions present within the surface-treated steel foil were detected by leakage magnetic flux testing using a micro-internal defect detector. The device (novel IDD) disclosed in "Toyo Kohan Vol. 33, pages 17-22" was used as the micro-internal defect detector. Specifically, the size and number of nonmetallic inclusions were measured after nickel plating the steel sheet and before the first rolling. The thickness of the nickel-plated steel sheet at the time of measurement was 100-300 μm. After the measurement, the thickness of the sheet when rolled to the thickness of this embodiment was measured. 2 When converted to the number of nonmetallic inclusions with a size of φ50 μm or larger contained within, the evaluation can be performed as follows. Particularly preferred: 10 pieces / 1000m 2 below Even more preferable: 20 pieces / thousandm 2 below More preferable: 30 pieces / thousand m 2 below Preferred: 40 pieces / thousand m 2 below Practical: 50 units / 1000m 2 below

[0102] <Example 1> First, a cold-rolled steel sheet (170 μm thick) of low-carbon aluminum-killed steel having the chemical composition shown below was prepared as the base material 20. C: 0.049% by weight, Mn: 0.33% by weight, Si: 0.003% by weight, P: 0.012% by weight, S: 0.009% by weight, Al: 0.047% by weight, balance: Fe and inevitable impurities.

[0103] Next, the prepared raw material was subjected to electrolytic degreasing and pickling by sulfuric acid immersion. Then, nickel plating was performed under the conditions described below to form nickel plating layers on both sides with the target thickness as shown in the table (nickel plating process). The conditions for nickel plating were as follows. (Conditions for Ni plating) Bath composition: Watt bath Nickel sulfate hexahydrate: 250g / L Nickel chloride hexahydrate: 45 g / L Boric acid: 30g / L Bath temperature: 60℃ pH: 4.0~5.0 Agitation: Air agitation or jet agitation Current density: 10A / dm 2

[0104] The amount of nickel deposited was measured using an X-ray fluorescence spectrometer. Similarly, after the second heat treatment process and after the second rolling process (described later), the amount of nickel deposited was determined using the same X-ray fluorescence spectrometer. A Rigaku ZSX100e X-ray fluorescence spectrometer was used.

[0105] Next, the steel sheet having the nickel plating layer formed above was subjected to continuous annealing under the conditions of a heat treatment temperature of 660°C, a soaking time of 30 seconds, and a reducing atmosphere to obtain a treated steel sheet (first heat treatment step).

[0106] Next, the treated steel sheet was rolled to obtain rolled steel foil (first rolling process). The rolling conditions at this time were cold rolling with a reduction ratio of 65.0% or more and less than 70.0%. Subsequently, the treated steel sheet after the first rolling process was annealed at 590°C for a soaking time of 8 hours, for a total of 80 hours, to obtain surface-treated steel foil (second heat treatment process).

[0107] Next, the surface-treated steel foil after the second heat treatment process was rolled under the condition of a reduction ratio of 10.0% or more and less than 15.0% (second rolling process). The total reduction ratio calculated from the thickness before the first rolling process and the thickness after the second rolling process was 70.0% or more and less than 75.0%. The extreme density, crystallite size, corrosion resistance, mechanical properties, non-metallic inclusions, etc. of the obtained surface-treated steel foil are shown in Table 2.

[0108] <Example 2> First, the thickness of the base plate 20 was set to 180 μm, and nickel plating was performed in the same manner as in Example 1, except that the target thickness of the nickel plating was changed as shown in the table (nickel plating process).

[0109] Next, the steel sheet having the nickel plating layer formed above was subjected to continuous annealing under the conditions of a heat treatment temperature of 680°C, a soaking time of 30 seconds, and a reducing atmosphere (first heat treatment step) to obtain a treated steel sheet. The treated steel sheet obtained as described above was subjected to rolling (first rolling step) to obtain rolled steel foil. The rolling was carried out by cold rolling with a reduction ratio of 65.0% or more and less than 70.0%.

[0110] The rolled steel foil after the first rolling process described above was annealed in a reducing atmosphere at 590°C for 8 hours of soaking time, for a total of 80 hours (second heat treatment process). Next, the surface-treated steel foil after the second heat treatment process was rolled with a reduction ratio of 10.0% or more and less than 15.0% (second rolling process). The total reduction ratio calculated from the thickness before the first rolling process and the thickness after the second rolling process was 70.0% or more and less than 75.0%. The extreme density, crystallite size, corrosion resistance, mechanical properties, nonmetallic inclusions, etc. of the obtained surface-treated steel foil are shown in Table 2.

[0111] <Example 3> Nickel plating was performed in the same manner as in Example 1, except that the target thickness of the nickel plating was varied as shown in the table (nickel plating process). Next, the steel sheet having the nickel plating layer formed above was subjected to continuous annealing under the conditions of a heat treatment temperature of 680°C, a soaking time of 30 seconds, and a reducing atmosphere (first heat treatment step) to obtain a treated steel sheet. The treated steel sheet obtained as described above was subjected to rolling (first rolling step) to obtain rolled steel foil. The rolling was carried out by cold rolling with a reduction ratio of 65.0% or more and less than 70.0%.

[0112] The rolled steel foil after the first rolling process described above was annealed in a reducing atmosphere at 590°C for 8 hours of soaking time, for a total of 80 hours (second heat treatment process). Next, the surface-treated steel foil after the second heat treatment process was rolled with a reduction ratio of 10.0% or more and less than 15.0% (second rolling process). The total reduction ratio calculated from the thickness before the first rolling process and the thickness after the second rolling process was 70.0% or more and less than 75.0%. The extreme density, crystallite size, corrosion resistance, mechanical properties, nonmetallic inclusions, etc. of the obtained surface-treated steel foil are shown in Table 2.

[0113] <Example 4> Nickel plating was performed in the same manner as in Example 1, except that the thickness of the original plate was varied as shown in Table 1 (nickel plating process). Next, the steel sheet having the nickel plating layer formed above was subjected to continuous annealing under the conditions of a heat treatment temperature of 680°C, a soaking time of 30 seconds, and a reducing atmosphere (first heat treatment step) to obtain a treated steel sheet. The treated steel sheet obtained as described above was subjected to rolling (first rolling step) to obtain rolled steel foil. The rolling was carried out by cold rolling with a reduction ratio of 65.0% or more and less than 70.0%.

[0114] The rolled steel foil after the first rolling process described above was annealed in a reducing atmosphere at 590°C for 8 hours of soaking time, for a total of 80 hours (second heat treatment process). Next, the surface-treated steel foil after the second heat treatment process was rolled under the condition of a reduction ratio of 35.0% or more and less than 40.0% (second rolling process). The total reduction ratio calculated from the thickness before the first rolling process and the thickness after the second rolling process was 80.0% or more and less than 85.0%. The extreme density, crystallite size, corrosion resistance, mechanical properties, non-metallic inclusions, etc. of the obtained surface-treated steel foil are shown in Table 2.

[0115] <Example 5> Nickel plating was performed in the same manner as in Example 1, except that the thickness of the base plate 20 was set to 200 μm and the target thickness of the nickel plating was set as shown in the table (nickel plating process). Next, the steel sheet having the nickel plating layer formed above was heat-treated by continuous annealing under the conditions of a heat treatment temperature of 780°C, a soaking time of 30 seconds, and a reducing atmosphere (first heat treatment process) to obtain a treated steel sheet. The treated steel sheet obtained as described above was subjected to rolling (first rolling step) to obtain rolled steel foil. The rolling was carried out by cold rolling with a reduction ratio of 70.0% or more and less than 72.0%. The rolled steel foil following the first rolling process described above was annealed in a reducing atmosphere at 560°C for 8 hours of soaking time, for a total of 80 hours (second heat treatment process). The second rolling process was not performed. The total reduction ratio calculated from the thickness before the first rolling process and the thickness after the second rolling process was between 70.0% and 75.0%. The extreme density, crystallite size, corrosion resistance, mechanical properties, nonmetallic inclusions, etc. of the obtained surface-treated steel foil are shown in Table 2.

[0116] <Example 6> The procedure was the same as in Example 1, except that the thickness of the raw material was as shown in Table 1 and the second rolling process was omitted. The results are shown in Table 2.

[0117] <Example 7> First, a cold-rolled steel sheet (180 μm thick) of low-carbon aluminum-killed steel having the chemical composition shown below was prepared as the base material 20. C: 0.052% by weight, Mn: 0.34% by weight, Si: 0.001% by weight or less, P: 0.012% by weight, S: 0.007% by weight, Al: 0.05% by weight, balance: Fe and inevitable impurities. The procedure was the same as in Example 1, except that the heat treatment temperature for the first heat treatment step was set to 680°C and the heat treatment temperature for the second heat treatment step was set to 580°C. The results are shown in Table 2.

[0118] <Example 8> The procedure was the same as in Example 7, except that a nickel plating with a target thickness of 0.6 μm on both sides was added to the surface as a re-plating. The results are shown in Table 2. Here, the nickel plating conditions for the re-plating were the same as those described above, and the target thickness was achieved by controlling the energizing time. The strike nickel plating conditions shown below were used as a pretreatment for the re-plating nickel plating. <Strike Nickel Plating Conditions> ·Bath composition: Nickel sulfate hexahydrate: 250g / L Sulfuric acid: 50g / L ·Bath temperature: 60℃ ·Current density: 30A / dm 2 Plating time: 5 seconds

[0119] <Example 9> First, a cold-rolled steel sheet (180 μm thick) of low-carbon aluminum-killed steel having the chemical composition shown below was prepared as the base material 20. C: 0.040% by weight, Mn: 0.35% by weight, Si: 0.01% by weight, P: 0.013% by weight, S: 0.018% by weight, Al: 0.047% by weight, balance: Fe and inevitable impurities. The procedure was the same as in Example 8, except that the above-mentioned original plate was used. The results are shown in Table 2.

[0120] <Comparative Example 1> The procedure was carried out in the same manner as in Example 4, except that the reduction ratios for the first and second rolling processes were changed. The results are shown in Tables 1 and 2.

[0121] <Reference example> The procedure was the same as in Example 5, except that the nickel plating process and the process after the first heat treatment were omitted. The results are shown in Tables 1 and 2.

[0122] [Table 1]

[0123] [Table 2]

[0124] [Table 3]

[0125] The above examples and comparative examples demonstrate that the surface-treated steel foil produced by this example exhibits high corrosion resistance. On the other hand, the surface-treated steel foil of the comparative examples was shown to fail to achieve the required corrosion resistance. Furthermore, in this embodiment, it was shown that when the crystallite size is below a predetermined value, the yield strength increases and the yield elongation is suppressed. This indicates that fatigue strength and processability can be improved. [Industrial applicability]

[0126] As described above, the surface-treated steel foil of the present invention can be applied to a wide range of industries, including secondary batteries, automobiles, and electronic devices. [Explanation of Symbols]

[0127] 10 Surface-treated steel foil 20 Base material 30 Iron-nickel alloy layer

Claims

1. Steel plate and, A surface-treated steel foil having an iron-nickel alloy layer formed on at least one surface of the steel plate, On the outermost surface of the surface of the surface-treated steel foil having an iron-nickel alloy layer, an iron-nickel alloy or nickel is present. The <001> pole density in the inverse pole diagram in the rolling direction at the outermost surface of the surface having the iron-nickel alloy layer is greater than the <111> pole density, and The density of the <001> pole in the inverse pole diagram in the rolling direction at the outermost surface of the surface having the iron-nickel alloy layer is greater than the density of the <101> pole. A surface-treated steel foil characterized by the following features.

2. The surface-treated steel foil according to claim 1, wherein the <111> pole density of the inverse pole diagram in the rolling direction is less than 3.

0.

3. The surface-treated steel foil according to claim 1 or 2, wherein the crystallite size of the nickel (220) plane or the (220) plane of the iron-nickel alloy on the surface having the iron-nickel alloy layer is 45 nm or less.

4. The surface-treated steel foil according to claim 1 or 2, wherein the <001> pole density of the inverse pole diagram in the rolling direction at the outermost surface of the surface having the iron-nickel alloy layer is 1.3 or more.

5. The number of nonmetallic inclusions with a size of φ50 μm or larger contained within is 50 per 1000 m ２ The surface-treated steel foil according to claim 1 or 2, which is as follows:

6. The surface-treated steel foil according to claim 1 or 2, wherein an iron-nickel alloy layer is formed on both sides of the steel plate.

7. The surface-treated steel foil according to claim 1 or 2, wherein the tensile strength is 400 MPa or more and 550 MPa or less.

8. The surface-treated steel foil according to claim 1 or 2, wherein the yield strength is 360 MPa or higher.

9. A surface-treated steel foil according to claim 1 or 2, wherein the elongation rate is 3% or more.

10. In the surface having the iron-nickel alloy layer, the amount of nickel deposited is 1.5 g / m². ２ ~30.0 g / m ２ The surface-treated steel foil according to claim 1 or 2.

11. A surface-treated steel foil according to claim 1 or 2, wherein the thickness is less than 100 μm.

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