Ni-plated surface-treated steel sheet and battery container

Abstract

Provided is an Ni-plated surface-treated steel sheet comprising a steel sheet and an Fe-Ni-Cu-Cr layer formed on at least one surface of the steel sheet, wherein, when the Cu intensity is continuously measured in the depth direction from the front surface side of the Fe-Ni-Cu-Cr layer by radio-frequency glow discharge optical emission spectrometry (GDS), the ratio IRCu-0.1d of the Cu intensity InCu-0.1d at a position 0.1 μm in depth from the front surface side with respect to the Cu intensity InCu-steel in the steel sheet is at least 0.5 and less than 3.0.

Description

[Technical Field]

[0001] This invention relates to nickel-plated surface-treated steel sheets and battery containers. [Background technology]

[0002] Conventionally, nickel-plated steel sheets containing nickel have been widely used as a material for battery containers. Patent Document 1 discloses a nickel-plated steel sheet for battery containers that has an Fe-Ni diffusion layer formed by applying a nickel plating layer to the steel sheet and then performing a thermal diffusion treatment to prevent pitting corrosion and leakage, and in which the ratio of Ni to Fe in the outermost layer is controlled. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-47359 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, with the increasing capacity of batteries, the battery container using Ni-plated steel sheets disclosed in Patent Document 1 had a problem: when over-discharge occurred due to a malfunction in the battery management system, the potential of the Fe-Ni diffusion layer approached the positive electrode potential, causing iron to dissolve from the Fe-Ni diffusion layer into the electrolyte, which could corrode the inner wall of the battery container. In the future, as battery capacity increases, the positive electrode potential is expected to rise even further, and there is a need for Ni-plated steel sheets with even better electrolyte resistance during over-discharge.

[0005] The objective of the present invention is to provide a Ni-plated surface-treated steel sheet with excellent electrolyte resistance during over-discharge. [Means for solving the problem]

[0006] As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by forming an Fe-Ni-Cu-Cr layer on the surface of a Ni-plated steel sheet, and have completed the present invention.

[0007] [1] According to Aspect 1 of the present invention, there is provided a Ni-plated steel sheet including a steel sheet and an Fe-Ni-Cu-Cr layer formed on at least one surface of the steel sheet, wherein when continuously measuring the Cu intensity in the depth direction from the surface side of the Fe-Ni-Cu-Cr layer by high-frequency glow discharge optical emission spectroscopy (GDS), the ratio IR of the Cu intensity In at a position 0.1 μm deep from the surface side to the Cu intensity In in the steel sheet Cu-steel is 0.5 or more and less than 3.0. Cu-0.1d of Cu-0.1d is provided.

[0008] [2] According to Aspect 2 of the present invention, there is provided the Ni-plated steel sheet of Aspect 1, wherein when continuously measuring the Cu intensity in the depth direction from the surface side of the Fe-Ni-Cu-Cr layer by high-frequency glow discharge optical emission spectroscopy (GDS), the ratio IR of the Cu intensity In at a position 0.5 μm deep from the surface side to the Cu intensity In in the steel sheet Cu-steel is 0.5 or more and less than 3.0. Cu-0.5d of Cu-0.5d is provided.

[0009] [3] According to Aspect 3 of the present invention, there is provided the Ni-plated steel sheet of Aspect 1 or 2, wherein when continuously measuring the Cr intensity in the depth direction from the surface side of the Fe-Ni-Cu-Cr layer by high-frequency glow discharge optical emission spectroscopy (GDS), the ratio IR of the Cr intensity In at a position 0.5 μm deep from the surface side to the Cr intensity In in the steel sheet Cr-steel is 0.2 or more and less than 2.0. Cr-0.5d of Cr-0.5d is provided.

[0010] [4] According to aspect 4 of the present invention, when the Cr intensity of the Fe-Ni-Cu-Cr layer is continuously measured from the surface side toward the depth direction by high-frequency glow discharge emission spectroscopy (GDS), the Cr intensity in the steel sheet is measured. Cr-steel Cr intensity at a depth of 0.1 μm from the surface side relative to In Cr-0.1d Ratio IR Cr-0.1d However, a Ni-plated surface-treated steel sheet is provided in any of embodiments 1 to 3, wherein the ratio is 0.2 or more and less than 2.0.

[0011] [5] According to aspect 5 of the present invention, when the Cu intensity of the Fe-Ni-Cu-Cr layer is continuously measured from the surface side toward the depth direction by radio frequency glow discharge emission spectroscopy (GDS), the Cu intensity of the steel sheet In Cu-steel Cu intensity at a depth of 0.3-0.7 μm from the surface side relative to In Cu-0.3d~0.7d Ratio IR Cu-0.3d~0.7d However, a Ni-plated surface-treated steel sheet is provided in any of embodiments 1 to 4, wherein the value is between 0.5 and 3.0.

[0012] [6]According to aspect 6 of the present invention, a Ni-plated surface-treated steel sheet of any of aspects 1 to 5 is provided, wherein the Fe-Ni-Cu-Cr layer has a Cu-enriched region.

[0013] [7] According to aspect 7 of the present invention, when the Cu intensity of the Fe-Ni-Cu-Cr layer is continuously measured from the surface side toward the depth direction by high-frequency glow discharge emission spectroscopy (GDS), the maximum Cu intensity In is measured at the depth to the steel plate. MAX The Cu strength in the steel plate, Cu-steel Ratio IR Cu-MAX However, a Ni-plated surface-treated steel sheet is provided in any of embodiments 1 to 6, wherein the value is greater than 0.8 and less than or equal to 3.0.

[0014] [8] According to aspect 8 of the present invention, a Ni-plated surface-treated steel sheet is provided, wherein the steel sheet is low-carbon steel or extremely low-carbon steel, according to any of aspects 1 to 7.

[0015] [9]According to aspect 9 of the present invention, a Ni-plated surface-treated steel sheet is provided, wherein the steel sheet is low-carbon steel, the Cu content in the steel sheet is 0.01% by weight to 1.0% by weight, and the Cr content in the steel sheet is 0.01% by weight to 1.0% by weight.

[0016]

[10] According to aspect 10 of the present invention, a battery container is provided which is made of a Ni-plated surface-treated steel sheet according to any of aspects 1 to 9. [Effects of the Invention]

[0017] According to the present invention, it is possible to suppress the dissolution of metals such as iron (Fe) into the electrolyte during over-discharge, and to provide a Ni-plated surface-treated steel sheet with excellent electrolyte resistance. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a schematic cross-sectional view showing the structure of a Ni-plated surface-treated steel sheet in an embodiment of the present invention. [Figure 2] Figure 2 shows an example of a temperature profile of a plated steel sheet to illustrate the method for calculating the thermal history Y in a thermal diffusion treatment. [Figure 3] Figure 3(a) is a chart obtained by high-frequency glow discharge emission spectroscopy of Example 1, and Figure 3(b) is an enlarged view of the chart obtained by high-frequency glow discharge emission spectroscopy of Example 1. [Figure 4] Figure 4(a) is a chart obtained by high-frequency glow discharge emission spectroscopy in Example 2, and Figure 4(b) is an enlarged view of the chart obtained by high-frequency glow discharge emission spectroscopy in Example 2. [Figure 5] Figure 5(a) is a chart obtained by high-frequency glow discharge emission spectroscopy of Comparative Example 1, and Figure 5(b) is an enlarged view of the chart obtained by high-frequency glow discharge emission spectroscopy of Comparative Example 1. [Figure 6] Figure 6 is a schematic diagram of a measuring jig used for evaluating the electrolyte resistance of Ni-plated surface-treated steel sheets using the LSV method. [Modes for carrying out the invention]

[0019] Figure 1 is a schematic cross-sectional view showing the structure of the Ni-plated surface-treated steel sheet in this embodiment. As shown in Figure 1, the Ni-plated surface-treated steel sheet 1 in this embodiment comprises a steel sheet 2 made of carbon steel and an Fe-Ni-Cu-Cr layer 3 formed on at least one surface of the steel sheet 2.

[0020] The steel sheet 2, which is the base material for the Ni-plated surface-treated steel sheet 1, is made of carbon steel. The carbon steel used for the steel sheet 2 is not particularly limited as long as it is a carbon steel with excellent formability, but for example, low carbon steel such as low-carbon aluminum-killed steel (carbon content 0.01% to 0.15% by weight) in which the carbon content is controlled by aluminum during steel manufacturing, ultra-low carbon steel with a carbon content of less than 0.01% by weight, or non-aging ultra-low carbon steel made by adding Ti or Nb to ultra-low carbon steel can be used.

[0021] As for the steel sheet 2, among these, a base sheet made of carbon steel containing a predetermined amount of Cu and Cr can be suitably used, from the viewpoint of being able to diffuse the Cu and Cr in the base sheet used as the steel sheet 2 into the Ni plating to form the Fe-Ni-Cu-Cr layer 3. The Cu content in the steel sheet 2 is preferably 0.01% to 1.0% by weight, more preferably 0.05% to 1.0% by weight, even more preferably 0.05% to 0.5% by weight, and particularly preferably 0.1% to 0.4% by weight, from the viewpoint of being able to further suppress metal elution by increasing the amount of Cu in the Fe-Ni-Cu-Cr layer 3. However, when the surface-treated steel sheet 1 is used for cylindrical containers etc. that undergo deep drawing or the like in forming, the Cu content in the steel sheet 2 is preferably 0.05% to 0.4% by weight.

[0022] The Cr content in the steel sheet 2 is preferably 0.01% to 1.0% by weight, more preferably 0.03% to 1.0% by weight from the viewpoint of increasing the amount of Cr in the Fe-Ni-Cu-Cr layer 3 to further suppress metal leaching, even more preferably 0.03% to 0.5% by weight from the viewpoint of reducing the decrease in electrical conductivity on the surface of the Fe-Ni-Cu-Cr layer 3 and suppressing metal leaching, and particularly preferably 0.03% to 0.4% by weight. The method for adjusting the respective Cu and Cr content in the steel sheet 2 is not particularly limited, but for example, a method can be used in which steel material produced from raw materials including carbon steel scrap and iron scrap containing SUS or Cu wire is used as the base sheet for the steel sheet 2.

[0023] In this embodiment, the base material for steel sheet 2 may be a hot-rolled carbon steel sheet that has been pickled to remove surface scale (oxide film), then cold-rolled, followed by electrolytic cleaning such as alkaline electrolytic degreasing, and then annealed and / or temper-rolled, or a sheet that has been cold-rolled, electrolytically cleaned, and then not annealed or temper-rolled. Furthermore, from the viewpoint of productivity, it is preferable to use a continuous steel strip as steel sheet 2. The hot-rolled sheet may be manufactured using a blast furnace or an electric furnace.

[0024] In this embodiment, as Fe, Cu, and Cr diffuse from the surface of the base sheet of steel sheet 2 during the heat diffusion treatment process described later, the Cu and Cr content near the boundary between the Fe-Ni-Cu-Cr layer 3 and steel sheet 2 decreases. However, the region where the Cu and Cr content decreases is only a small part of the total thickness of steel sheet 2, and has almost no effect on the overall component ratio of steel sheet 2. Therefore, it is acceptable to recognize that the Cu and Cr content in steel sheet 2 is the same as the Cu and Cr content in the base sheet. Similarly, for components other than Cu and Cr, the component ratio of steel sheet 2 and the component ratio of steel sheet 2 can be recognized as being approximately the same before and after the heat diffusion treatment process. In other words, the base sheet for steel plate 2 is not particularly limited, and can be any carbon steel with excellent formability, similar to steel plate 2. For example, low-carbon steel such as low-carbon aluminum-killed steel (carbon content 0.01% to 0.15% by weight) in which the carbon content is controlled by aluminum during steel manufacturing, extremely low-carbon steel with a carbon content of less than 0.01% by weight, or non-aging extremely low-carbon steel obtained by adding Ti or Nb to extremely low-carbon steel can be used. From the viewpoint of being able to diffuse Cu and Cr in the base sheet into the Ni plating to form the Fe-Ni-Cu-Cr layer 3, a base sheet made of carbon steel containing a predetermined amount of Cu and Cr can be suitably used.

[0025] The thickness of the steel sheet 2 can be appropriately selected according to the application of the Ni-plated surface-treated steel sheet 1 and is not particularly limited, but from the viewpoint of reducing manufacturing costs, it is preferably 1.5 mm or less, more preferably 1.25 mm or less, and even more preferably 0.9 mm or less. Furthermore, from the viewpoint of improving the mechanical properties of the Ni-plated surface-treated steel sheet 1, the thickness of the steel sheet 2 is preferably 0.03 mm or more, more preferably 0.1 mm or more, even more preferably 0.15 mm or more, and particularly preferably 0.2 mm or more.

[0026] The Ni-plated surface-treated steel sheet 1 of this embodiment is provided with an Fe-Ni-Cu-Cr layer 3 on the steel sheet 2. The Fe-Ni-Cu-Cr layer 3 is formed by forming a Ni plating layer on the steel sheet 2, and then performing a thermal diffusion treatment on the steel sheet 2 with the Ni plating layer, thereby causing thermal diffusion between the iron (Fe), copper (Cu), and chromium (Cr) constituting the steel sheet 2 and the nickel (Ni) constituting the Ni plating layer. The Fe-Ni-Cu-Cr layer 3 only needs to be formed on at least one surface of the steel sheet 2, or it may be formed on both sides of the steel sheet 2. The Ni-plated surface-treated steel sheet 1 of this embodiment has excellent electrolyte resistance during over-discharge due to the provision of the Fe-Ni-Cu-Cr layer 3.

[0027] The presence of an Fe-Ni-Cu-Cr layer 3 in the Ni-plated surface-treated steel sheet 1 can be confirmed by performing elemental analysis on the surface layer of the Ni-plated surface-treated steel sheet 1. Specifically, this can be confirmed by performing surface composition analysis using methods such as high-frequency glow discharge emission spectroscopy (GDS), Auger electron spectroscopy (AES), and X-ray photoelectric spectroscopy (XPS). For example, high-frequency glow discharge emission spectroscopy is performed in the depth direction from the surface toward the steel sheet 2 on a standard sample of low-carbon steel with a Ni-plated layer formed on it, and on the Ni-plated surface-treated steel sheet 1, and the changes in Fe intensity, Ni intensity, Cu intensity, and Cr intensity with respect to measurement time are continuously measured. In the obtained data, when comparing each intensity of the standard sample with each intensity of the Ni-plated surface-treated steel sheet 1, it can be determined that Fe is present if the Fe intensity of the Ni-plated surface-treated steel sheet 1 is in the range where the Fe intensity is 10% or more of the maximum Fe intensity of the standard sample. Similarly, it can be determined that Ni is present if the Ni intensity of the Ni-plated surface-treated steel sheet 1 is in the range where the Ni intensity is 10% or more of the maximum Ni intensity of the standard sample. Furthermore, if the Cu strength at any depth in the Ni-plated steel sheet 1 is higher than the Cu strength at the same depth in the Ni-plated layer of the standard sample, it can be determined that Cu is present at that depth. Similarly, if the Cr strength at any depth in the Ni-plated steel sheet 1 is higher than the Cr strength at the same depth in the Ni-plated layer of the standard sample, it can be determined that Cr is present at that depth. If there is a location where Fe, Ni, Cu, and Cr can be determined to be present, it can be determined that an Fe-Ni-Cu-Cr layer 3 is formed at that location. The standard sample will be described in more detail later.

[0028] Furthermore, since the Cu and Cr in the Fe-Ni-Cu-Cr layer 3 diffused from the base sheet used as steel sheet 2, the proportion of Cu and Cr present in the Fe-Ni-Cu-Cr layer 3 is very small compared to the proportion of Fe and Ni. In other words, the proportions of Fe and Ni are dominant in the metallic composition of the Fe-Ni-Cu-Cr layer 3. Specifically, the Cu and Cr content in the Fe-Ni-Cu-Cr layer 3 is approximately the same as or less than the Cu and Cr content in steel sheet 2, so the total amount of Cu and Cr is 2% by weight or less, and the total amount of iron and nickel is 98% by weight or more.

[0029] The Ni-plated surface-treated steel sheet 1 only needs to have an Fe-Ni-Cu-Cr layer 3, but the Cu intensity in the steel sheet 2 measured by high-frequency glow discharge emission spectroscopy is In Cu-steel Cu intensity at a depth of 0.5 μm from the surface side relative to In Cu-0.5d Ratio IR Cu-0.5d (=In Cu-0.5d / In Cu-Steel ) is preferably 0.50 or more and less than 3.0. Cu intensity ratio IR Cu-0.5d By keeping the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge. The reason for this is not entirely clear, but it is thought that a mixed potential can be achieved at the surface of the Fe-Ni-Cu-Cr layer 3, suppressing localized dissolution when in contact with the electrolyte. If there is too little Cu near the surface, the number of crystal grains containing Cu at the surface of the Fe-Ni-Cu-Cr layer 3 will decrease, or the region where Cu exists will become smaller, which may prevent a sufficient mixed potential from being achieved. Also, if there is too much Cu near the surface, areas with locally noble potential will occur in the Fe-Ni-Cu-Cr layer 3, widening the potential difference with Fe and potentially increasing the dissolution of metals such as iron. From the viewpoint of further suppressing the dissolution of metals such as iron during over-discharge, the intensity ratio IR Cu-0.5d The lower limit is more preferably 0.7 or higher, and even more preferably 0.8 or higher, and the intensity ratio IR Cu-0.5dThe upper limit is more preferably 2.5 or less, even more preferably 2.0 or less, and particularly preferably 1.8 or less. The Cu strength In in the steel sheet 2 Cu-steel The method for obtaining it will be described in detail later. In particular, when the Ni deposition amount is relatively small, making the strength ratio IR Cu-0.5d fall within the above range is important for improving the electrolyte resistance during over-discharge.

[0030] In high-frequency glow discharge optical emission spectroscopy, the intensity of each element at each depth position is determined by calculating the depth from the sample surface by converting using the measurement time (etching time) and the etching rate by sputtering (unit: μm / second), and reading the intensity at that position. In this embodiment, the measurement time is converted to the measurement depth using the etching rate of Ni. The method for converting the measurement time to the measurement depth is specifically as follows.

[0031] First, the etching rate of Ni is determined. To determine the etching rate of Ni, a standard sample made of a steel sheet with unannealed Ni plating whose plating layer thickness (or deposition amount) is known is prepared. For example, a standard Ni-plated steel sheet obtained by applying matte Ni plating with a thickness of 1.1 μm to a low-carbon steel sheet with a thickness of 0.3 mm is prepared. The plating treatment for applying matte Ni plating to the standard Ni-plated steel sheet is not particularly limited, but for example, it can be performed using the following Watts bath. <Ni plating conditions> Bath composition: Nickel sulfate hexahydrate 250 g / L, Nickel chloride hexahydrate 45 g / L, Boric acid 30 g / L pH: 4.0 - 5.0 Bath temperature: 60 °C Current density: 10 A / dm 2 The thickness of the Ni plating on a standard Ni-plated steel sheet can be determined by measuring the thickness through cross-sectional observation of the steel sheet with the Ni plating layer using a scanning electron microscope (SEM), or by converting the amount of Ni deposited, determined by X-ray fluorescence analysis, into thickness using the specific gravity of Ni. For this standard sample, the Fe intensity and Ni intensity in the standard Ni-plated steel sheet are measured from the Ni-plated side using a high-frequency glow discharge emission spectrometer until the Fe intensity reaches saturation, and a chart is obtained. From the obtained chart, the etching time of the Ni plating layer is determined. Specifically, the time from the start of measurement until the Fe intensity reaches 10% of its saturation value is defined as the Ni etching time. From the Ni etching time and the thickness of the Ni plating layer, the Ni etching rate can be determined. The saturation value of the Fe intensity is determined from the rate of change of Fe intensity over time (Fe intensity change / second). The rate of change of Fe intensity over time increases sharply when Fe is detected after the start of measurement, decreases after passing the maximum value, and stabilizes near zero. The value of the Fe intensity when the rate of change over time stabilizes near zero is the saturation value of the Fe intensity. Specifically, when the rate of change of Fe intensity over time falls below 0.02 (Fe intensity / second), the Fe intensity can be considered saturated.

[0032] The etching rate of Ni determined as described above is a parameter that shows the relationship between the depth time (measurement time by high-frequency glow discharge emission spectrometer) obtained by measuring a steel sheet with a Ni plating layer formed on it without thermal diffusion treatment, where the Ni plating thickness is known, using a high-frequency glow discharge emission spectrometer, and the actual thickness. Therefore, using the etching rate of Ni determined as described above, the measurement time of high-frequency glow discharge emission spectrometer analysis for the Ni-plated surface-treated steel sheet 1 can be converted to etching depth (thickness). It is known that the etching rates of iron and nickel are approximately the same in measurements using a high-frequency glow discharge emission spectrometer. In addition, since the copper and chromium contained in the Fe-Ni-Cu-Cr layer 3 are diffused from the carbon steel base sheet, the amount of copper and chromium contained in the Fe-Ni-Cu-Cr layer 3 is trace, and copper and chromium have almost no effect on the etching rate. Therefore, the etching rates of the Fe-Ni-Cu-Cr layer 3 are dominated by iron and nickel, and the etching rate of Ni obtained using the pure Ni plating layer can be used as the etching rate for both the Fe-Ni-Cu-Cr layer 3 and the steel sheet 2.

[0033] For example, the Cu intensity at a depth of 0.5 μm from the surface side is In Cu-0.5d To determine the target depth, read the Cu intensity when the Ni etching rate multiplied by the measurement time equals 0.5 μm. Note that depending on the etching rate, the intensity at the depth may not always match the target value, so read the intensity within a range of ±0.03 μm from the target value. For example, the intensity within the range of 0.5 μm ± 0.03 μm can be treated as the intensity at a depth of 0.5 μm. The Cu intensity at other depths other than 0.5 μm, as described later, can be read in the same way.

[0034] In high-frequency glow discharge emission spectroscopy, measurements are taken continuously from the surface of the sample toward the depth. Therefore, when high-frequency glow discharge emission spectroscopy is performed on the Ni-plated steel sheet 1 in this embodiment, as shown in Figure 3(a), data showing fluctuations in Fe intensity, Ni intensity, Cu intensity, and Cr intensity is obtained. Subsequently, the depth change (time change) of each of the Fe, Ni, Cu, and Cr intensity approaches zero, and in particular, data showing that the Fe intensity is nearly saturated is obtained. Furthermore, the Ni-plated steel sheet 1 has a structure in which an Fe-Ni-Cu-Cr layer 3 and a steel sheet 2 are laminated, and in the steel sheet 2, the concentration of each metal is usually constant in the depth direction. Therefore, the intensity data at points where such depth change amounts are close to zero represent the intensity data of each metal in the steel sheet 2. Furthermore, when comparing the results of high-frequency glow discharge emission spectroscopy for the Ni-plated steel sheet 1 and a standard sample in this embodiment, in the measurement results for the Ni-plated steel sheet 1, the depth at which the Ni intensity of the Ni-plated steel sheet 1 becomes 2% of the maximum value of the Ni intensity of the standard sample (hereinafter referred to as D) is Ni2% In this case (also known as), the depth change amount of the strength data for each metal is close to 0. Therefore, in this embodiment, the depth D in the high-frequency glow discharge emission spectroscopy analysis results of the Ni-plated surface-treated steel sheet 1 Ni2% The strength of each metal in the above example is used as the strength data for each metal in steel plate 2. That is, the strength of Cu in steel plate 2 as described above. Cu-steel is, depth D Ni2% The strength of Cu can be determined in the same way for chromium. Cr-steel is, depth D Ni2% This can be determined as the Cr intensity. Figure 3(a) is a chart obtained by high-frequency glow discharge emission spectroscopy in Example 1, which will be described later.

[0035] In this embodiment, the boundary between the Fe-Ni-Cu-Cr layer 3 and the base steel sheet 2 is defined as the point where the Ni intensity measured on the Ni-plated surface-treated steel sheet 1 is 10% of the maximum Ni intensity of a standard sample measured under the same conditions, and the depth at that point is defined as the thickness of the Fe-Ni-Cu-Cr layer 3. The thickness of the Fe-Ni-Cu-Cr layer 3 is preferably 0.5 to 3.5 μm, and more preferably 0.7 to 3.0 μm.

[0036] In the steel plate 2 obtained in this way, Cu strength In Cu-steel Cu intensity at a depth of 0.5 μm from the surface side relative to In Cu-0.5d Ratio (IR) Cu-0.5d =In Cu-0.5d / In Cu-Steel This value represents the ratio of the Cu strength near the surface of the Fe-Ni-Cu-Cr layer 3 to the Cu strength in the steel sheet 2, and is an indicator of how far the Cu in the steel sheet 2 has diffused to the surface.

[0037] In a Ni-plated surface-treated steel sheet 1, the Cu intensity in the steel sheet 2 is measured by high-frequency glow discharge emission spectroscopy (GDS). Cu-steel Cu intensity at a depth of 0.1 μm from the surface side relative to In Cu-0.1d Ratio IR Cu-0.1d (=In Cu-0.1d / In Cu-steel The Cu intensity ratio IR is between 0.50 and less than 3.0. Cu-0.1d This represents the ratio of the Cu intensity near the outermost surface of the Fe-Ni-Cu-Cr layer 3 to the Cu intensity in the steel sheet 2, and is an indicator of how far the Cu in the steel sheet 2 has diffused to the outermost surface. If there is too little Cu near the outermost surface, the number of crystal grains containing Cu at the outermost surface of the Fe-Ni-Cu-Cr layer 3 will decrease, or the region where Cu exists will become smaller, which may prevent a sufficient hybridization potential from being achieved. On the other hand, if there is too much Cu near the outermost surface, metal dissolution may increase. From the perspective of further suppressing metal dissolution during over-discharge, the intensity ratio IR is used. Cu-0.1dThe lower limit is more preferably 0.6 or higher, even more preferably 0.7 or higher, and particularly preferably 0.8 or higher. Cu-0.1d The upper limit is more preferably 2.0 or less, even more preferably 1.5 or less, and particularly preferably less than 1.0. Cu intensity ratio IR Cu-0.1d By keeping the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge. In particular, the strength ratio IR Cu-0.1d By keeping this within the above range, even when the amount of Ni deposited is relatively small, the Ni-plated surface-treated steel sheet 1 can be made to have excellent electrolyte resistance during over-discharge.

[0038] In Ni-plated surface-treated steel sheet 1, the Cu intensity in steel sheet 2 is measured by high-frequency glow discharge emission spectroscopy. Cu-steel Cu intensity at a depth of 0.3 μm from the surface side relative to In Cu-0.3d Ratio IR Cu-0.3d (=In Cu-0.3d / In Cu-steel ) is preferably 0.50 or more and less than 3.0. From the viewpoint of further suppressing metal dissolution during over-discharge, the intensity ratio IR Cu-0.3d The lower limit is more preferably 0.7 or higher, even more preferably 0.8 or higher, and particularly preferably 0.9 or higher. Cu-0.3d The upper limit is more preferably 2.5 or less, even more preferably 2.0 or less, and particularly preferably 1.8 or less. Cu intensity ratio IR Cu-0.3d By keeping the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge. In particular, the strength ratio IR Cu-0.3d By setting this within the above range, even when the amount of Ni deposited is relatively small, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge.

[0039] In Ni-plated surface-treated steel sheet 1, the Cu intensity in steel sheet 2 is measured by high-frequency glow discharge emission spectroscopy. Cu-steel Cu intensity at a depth of 0.7 μm from the surface side relative to In Cu-0.7d Ratio IRCu-0.7d (=In Cu-0.7d / In Cu-steel ) is preferably 0.50 or more and less than 3.0. From the viewpoint of further suppressing metal dissolution during over-discharge, the intensity ratio IR Cu-0.7d The lower limit is more preferably 0.7 or higher, even more preferably 0.8 or higher, and particularly preferably 0.9 or higher. Cu-0.7d The upper limit is more preferably 2.5 or less, even more preferably 2.0 or less, and particularly preferably 1.8 or less. Cu intensity ratio IR Cu-0.7d By keeping the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge.

[0040] In Ni-plated surface-treated steel sheet 1, the Cu intensity in steel sheet 2 is measured by high-frequency glow discharge emission spectroscopy. Cu-steel Cu intensity at a depth of 0.9 μm from the surface side relative to In Cu-0.9d Ratio IR Cu-0.9d (=In Cu-0.9d / In Cu-steel ) is preferably 0.50 or more and less than 3.0. From the viewpoint of further suppressing metal dissolution during over-discharge, the intensity ratio IR Cu-0.9d The lower limit is more preferably 0.7 or higher, even more preferably 0.8 or higher, and particularly preferably 0.9 or higher. Cu-0.9d The upper limit is more preferably 2.5 or less, even more preferably 2.0 or less, and particularly preferably 1.8 or less. Cu intensity ratio IR Cu-0.9d By keeping the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge.

[0041] In Ni-plated surface-treated steel sheet 1, the Cu intensity in steel sheet 2 is measured by high-frequency glow discharge emission spectroscopy. Cu―steel The maximum value of Cu strength in the region from the surface to the boundary between the Fe-Ni-Cu-Cr layer 3 and the steel plate 2. Cu―MAX Ratio IR Cu-MAX (=In Cu―MAX / In Cu―steel) is preferably more than 0.8 and 3.0 or less. From the viewpoint of further enhancing the suppression of metal elution during over-discharge, IR Cu-MAX is more preferably 0.9 or more and 2.5 or less, still more preferably 0.9 or more and 2.0 or less, and particularly preferably 1.0 or more and 1.8 or less. The Cu strength ratio IR Cu-MAX being within the above range can make the Ni-plated surface-treated steel sheet 1 excellent in electrolytic solution resistance during over-discharge.

[0042] Further, in the Ni-plated surface-treated steel sheet 1, the Cu intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectrometry Cu-steel in the region from the surface to a depth of 0.3 μm to 0.7 μm with respect to the Cu intensity In Cu-0.3d~0.7d (that is, the Cu intensity measured at any depth position in the region from the surface to a depth of 0.3 μm to 0.7 μm) ratio IR Cu-0.3d~0.7d (= In Cu-0.3d~0.7d / In Cu-steel ) is preferably 0.5 or more and 3.0 or less. The Cu strength ratio IR Cu-0.3d~0.7d being within the above range can suppress the variation in the Cu content ratio in the depth direction of the Fe-Ni-Cu-Cr layer and make the mixed potential state more stable. As a result, the suppression of metal elution during over-discharge can be enhanced. From the viewpoint of further enhancing the suppression of metal elution by stably having a Cu-containing region not only at a specific depth position near the surface layer but also in the depth direction, the lower limit of the strength ratio IR Cu-0.3d~0.7d is more preferably 0.7 or more, still more preferably 0.8 or more, and particularly preferably 0.9 or more. Also, the upper limit of the strength ratio IR Cu-0.3d~0.7d is more preferably 2.5 or less, still more preferably 2.0 or less, and particularly preferably 1.8 or less. The Cu strength ratio IR Cu-0.3d~0.7d being within the above range can make the Ni-plated surface-treated steel sheet 1 excellent in electrolytic solution resistance during over-discharge.

[0043] The Fe-Ni-Cu-Cr layer 3 preferably has a Cu-enriched region formed in the intermediate region (i.e., the region deeper than the outermost surface of the Ni-plated surface-treated steel sheet 1 and shallower than the boundary point between the Fe-Ni-Cu-Cr layer 3 and the steel sheet 2). The fact that the Fe-Ni-Cu-Cr layer 3 has a Cu-enriched region can be confirmed, for example, by the Cu intensity In Cu-boundary at the position where it becomes the boundary between the Fe-Ni-Cu-Cr layer 3 and the steel sheet 2 which is the base material, and the Cu intensity In Cu-steel in the steel sheet 2, and the strength ratio IR Cu-boundary (=In Cu-boundary / In Cu-steel ) using the following equations (1) and (2). When the following equations (1) and (2) are satisfied, it can be determined that the Fe-Ni-Cu-Cr layer 3 has a Cu-enriched region in the intermediate region. In this case, the position where the Cu intensity becomes the maximum value is preferably between the position 0.3 μm deep from the surface and the position 0.1 μm shallower than the position where it becomes the boundary between the Fe-Ni-Cu-Cr layer 3 and the steel sheet 2 which is the base material. Also, the position where the Cu intensity becomes the maximum value is preferably at a depth from the surface that is 60% or less of the thickness of the Fe-Ni-Cu-Cr layer 3. By forming a Cu-enriched region in the intermediate region of the Fe-Ni-Cu-Cr layer 3, the Ni-plated surface-treated steel sheet 1 can be made excellent in electrolytic solution resistance during over-discharge. IR Cu-MAX -IR Cu-0.1d >0.05 (1) IR Cu-MAX -IR Cu-boundary >0.05 (2)

[0044] In the Ni-plated surface-treated steel sheet 1, the ratio IR Cu-0.5d-ref of the Cu intensity In Cu-d at an arbitrary depth position from the surface measured by high-frequency glow discharge optical emission spectrometry to the Cu intensity In Cu-d-vref at a depth of 0.5 μm measured by high-frequency glow discharge optical emission spectrometry of the standard sample (=In Cu-d / In Cu-0.5d-ref ) is preferably within a predetermined range. IR Cu-d-vrefPreferably, in the range of 0.1 μm to 0.5 μm depth from the surface, the IR is between 2.0 and 20. If the absolute amount of Cu near the outermost surface to the surface layer is too small, the number of crystal grains containing Cu in the Fe-Ni-Cu-Cr layer 3 will decrease, or the region where Cu exists will become smaller, which may prevent a sufficient hybridization potential from being achieved. Also, if the absolute amount of Cu near the outermost surface to the surface layer is too large, metal dissolution may increase. From the viewpoint of further suppressing metal dissolution during over-discharge, in the range of 0.1 μm to 0.5 μm depth from the surface (over the entire range of 0.1 μm to 0.5 μm depth from the surface), Cu-d-vref It is more preferably 2.3 or more and 10 or less, and even more preferably 3.0 or more and 10 or less. On the other hand, IR Cu-d-vref In the range where the depth from the surface is greater than 0.5 μm and less than or equal to 0.9 μm, the value is preferably 2.0 to 20, more preferably 2.5 to 15, and even more preferably 3.0 to 15.

[0045] In Ni-plated surface-treated steel sheet 1, specific IR Cu-MAX (=In Cu―MAX / In Cu―steel ) and, relative IR Cu-0.1d (=In Cu-0.1d / In Cu-steel ) difference IR Cu-MAX -IR Cu-0.1d However, it is preferably 1.0 or less, more preferably 0.6 or less, even more preferably 0.5 or less, and particularly preferably 0.3 or less. Cu-MAX -IR Cu-0.1d A smaller value indicates that within the Fe-Ni-Cu-Cr layer 3, the Cu intensity distribution is less varied, and Cu is diffused to near the outermost surface. Cu-MAX -IR Cu-0.1d By setting this within the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge, especially when the amount of Ni attached is relatively small.

[0046] In a Ni-plated surface-treated steel sheet 1, the Cr intensity in the steel sheet 2 is measured by high-frequency glow discharge emission spectroscopy (GDS). Cr-steel Cr intensity at a depth of 0.1 μm from the surface side relative to In Cr-0.1d Ratio IR Cr-0.1d (=In Cr-0.1d / In Cr-steel The Cr intensity ratio IR is preferably 0.2 or more and less than 2.0, more preferably 0.2 or more and less than 1.0, and even more preferably 0.2 or more and less than 0.95, from the viewpoint of suppressing metal dissolution due to the formation of hybrid potentials. Cr-0.1d By keeping the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge.

[0047] In a Ni-plated surface-treated steel sheet 1, the Cr intensity in the steel sheet 2 is measured by high-frequency glow discharge emission spectroscopy (GDS). Cr-steel Cr intensity at a depth of 0.3 μm from the surface side relative to In Cr-0.3d Ratio IR Cr-0.3d (=In Cr-0.3d / In Cr-steel ) is preferably 0.2 or more and less than 2.0, more preferably 0.2 or more and less than 0.95, and even more preferably 0.2 or more and less than 0.7. Cr intensity ratio IR Cr-0.3d By keeping the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge.

[0048] In a Ni-plated surface-treated steel sheet 1, the Cr intensity in the steel sheet 2 is measured by high-frequency glow discharge emission spectroscopy (GDS). Cr-steel Cr intensity at a depth of 0.5 μm from the surface side relative to In Cr-0.5d Ratio IR Cr-0.5d (=In Cr-0.5d / In Cr-steelThe Cr intensity ratio (IR) is preferably 0.2 or more and less than 2.0 from the viewpoint of diffusing Cr to the vicinity of the surface and stably achieving a sufficient hybrid potential. If there is too little Cr near the surface, the number of crystal grains containing Cr on the surface of the Fe-Ni-Cu-Cr layer 3 may decrease, or the region where Cr exists may become smaller. Also, if there is too much Cr near the surface, there may be areas where the potential difference with Fe widens locally. From the viewpoint of stably improving electrolyte resistance during over-discharge, it is more preferable that the ratio is 0.2 or more and less than 0.95, and even more preferable that it is 0.2 or more and less than 0.8. Cr-0.5d By keeping the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge.

[0049] In a Ni-plated surface-treated steel sheet 1, the Cr intensity in the steel sheet 2 is measured by high-frequency glow discharge emission spectroscopy (GDS). Cr-steel Cr intensity at a depth of 0.7 μm from the surface side relative to In Cr-0.7d Ratio IR Cr-0.7d (=In Cr-0.7d / In Cr-steel ) is preferably 0.2 or more and less than 2.0, more preferably 0.2 or more and less than 0.95, and even more preferably 0.2 or more and less than 0.8. Cr intensity ratio IR Cr-0.7d By keeping the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge.

[0050] In a Ni-plated surface-treated steel sheet 1, the Cr intensity in the steel sheet 2 is measured by high-frequency glow discharge emission spectroscopy (GDS). Cr-steel Cr intensity at a depth of 0.9 μm from the surface side relative to In Cr-0.9d Ratio IR Cr-0.9d (=In Cr-0.1d / In Cr-steel ) is preferably 0.2 or more and less than 2.0, more preferably 0.2 or more and less than 1.0, and even more preferably 0.2 or more and 0.95 or less. Cr intensity ratio IR Cr-0.9dBy keeping the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge.

[0051] In Ni-plated surface-treated steel sheet 1, the Cr intensity in steel sheet 2 is measured by high-frequency glow discharge emission spectroscopy. Cr―steel The maximum value of Cr intensity in the region from the surface to the boundary between the Fe-Ni-Cu-Cr layer 3 and the steel plate 2. Cr―MAX Ratio IR Cr-MAX (=In Cr―MAX / In Cr―steel ) is preferably 0.3 to 2.0, and more preferably 0.3 to 0.95. Cr intensity ratio IR Cr-max By keeping the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge.

[0052] Furthermore, in the Ni-plated surface-treated steel sheet 1, the Cr intensity in the steel sheet 2 is measured by high-frequency glow discharge emission spectroscopy. Cr-steel Cr intensity in the region from the surface to a depth of 0.3 μm to 0.7 μm relative to In Cu-0.3d~0.7d (i.e., the Cr intensity measured at any depth position in the region from 0.3 μm to 0.7 μm from the surface) IR ratio Cr-0.3d~0.7d (=In Cr-0.3d~0.7d / In Cr-steel ) is preferably 0.2 or more and 2.0 or less, and more preferably 0.2 or more and less than 0.95. Cr intensity ratio IR Cr-0.3d~0.7d By keeping the above range, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during over-discharge.

[0053] In a Ni-plated surface-treated steel sheet 1, the Cr intensity at a depth of 0.5 μm is measured by high-frequency glow discharge emission spectroscopy of a standard sample. Cr-0.5d-ref The Cr intensity at any depth from the surface, measured by high-frequency glow discharge emission spectroscopy, is determined for the following: Cr-d Ratio IR Cr-d-vref =(In Cr-d / In Cr-0.5d-ref) is preferably within a predetermined range. Cr-d-vref For depths from the surface in the range of 0.1 μm to 0.5 μm, the IR is preferably 2.0 to 30. If there is too little Cr near the outermost surface to the surface layer, the number of crystal grains containing Cr at the outermost surface of the Fe-Ni-Cu-Cr layer 3 will decrease, or the region where Cr exists will become smaller, which may prevent a sufficient hybrid potential from being achieved. Also, if there is too much Cr near the outermost surface to the surface layer, the electrical resistance of the surface may increase too much. For depths from the surface in the range of 0.1 μm to 0.5 μm, IR Cr-d-vref It is more preferable that it is between 2.5 and 30, even more preferable that it is between 5.5 and 30, and particularly preferable that it is between 7.0 and 20. On the other hand, IR Cr-d-vref For depths from the surface between 0.5 μm and 0.9 μm, the value is preferably 2.0 to 50, and more preferably 5.5 to 40.

[0054] In the Ni-plated surface-treated steel sheet 1, from the viewpoint of providing superior electrolyte resistance during over-discharge and good battery characteristics, the Cu strength of the steel sheet 2 is improved. Cu-steel The Cu strength at a depth of 0.5 μm from the surface side in the Fe-Ni-Cu-Cr layer 3 is In Cu-0.5d Ratio IR Cu-0.5d (=In Cu-0.5d / In Cu-Steel ) is 0.50 or more and less than 3.0, and the Cr strength in steel plate 2 is In Cr-steel Cr strength against In Cr-0.5d Ratio IR Cr-0.5d (=In Cr-0.5d / In Cr-steelPreferably, the ratio is between 0.2 and less than 2.0. By controlling both the Cu intensity ratio and the Cr intensity ratio to be within the above range, it is thought that the state of the hybrid potential due to the presence of Cu and Cr near the surface of the Fe-Ni-Cu-Cr layer 3 can be stabilized. Furthermore, even if Cr is present near the outermost surface or near the surface layer, the Fe-Ni-Cu-Cr layer 3 also contains Cu, which suppresses the increase in contact resistance. Combined with the suppression of metal leaching, this results in better battery characteristics.

[0055] In Ni-plated surface-treated steel sheet 1, the maximum value of Fe intensity was measured from the surface toward the steel sheet by high-frequency glow discharge emission spectroscopy for a standard sample (Ni-plated steel sheet). Fe―MAX-ref Fe strength at a depth of 0.1 μm from the surface side relative to 10% of the value In Fe-0.1d Ratio IR Fe-0.1d (=In Fe-0.1d / (0.1 × In Fe―MAX-ref )) is 1.0 or greater, but preferably 2.0 or greater and less than 7.0. IR Fe-0.1d By setting the range to the above range, the Fe-Ni-Cu-Cr layer can be formed over the entire surface of the wide or large surface-treated steel sheet 1, thereby stably improving electrolyte resistance.

[0056] In a Ni-plated surface-treated steel sheet 1, the lower limit of the amount of Ni deposited on the surface where the Fe-Ni-Cu-Cr layer 3 is formed as the outermost layer is 0.45 g / m², from the viewpoint of appropriately forming the Fe-Ni-Cu-Cr layer 3 and controlling the Cu strength ratio and Cr strength ratio between the steel sheet 2 and the Fe-Ni-Cu-Cr layer 3 within an appropriate range. 2 The above is preferable, 0.8 g / m 2 The above is more preferable, 2.5 g / m 2 The above is even more preferable, 3.0 g / m 2 The above is particularly preferable. In the Ni-plated surface-treated steel sheet 1, the upper limit of the amount of Ni deposited on the surface where the Fe-Ni-Cu-Cr layer 3 is formed as the outermost layer is 10.7 g / m², from the viewpoint that it becomes difficult for Fe to diffuse to the outermost surface, and that it becomes necessary to raise the heat treatment temperature or lengthen the heat treatment time in order to sufficiently diffuse Fe.2 The following is preferable: 8.9 g / m 2 Less than 8.0 g / m² is more preferable. 2 The following is even more preferable: 7.2 g / m 2 The following are particularly preferred. The amount of Ni deposited can be determined by X-ray fluorescence measurement. In X-ray fluorescence measurement, quantitative analysis is possible using a calibration curve method. X-ray fluorescence measurement may be performed on the Ni-plated surface-treated steel sheet 1 on which the Fe-Ni-Cu-Cr layer 3 is formed by thermal diffusion treatment, or on the steel sheet 2 on which the Ni-plated layer is formed before thermal diffusion treatment.

[0057] In this embodiment, as shown in Figure 1, the Fe-Ni-Cu-Cr layer 3 is formed on only one side of the steel sheet 2. However, the configuration of the Ni-plated surface-treated steel sheet 1 is not limited to this. The Fe-Ni-Cu-Cr layer 3 only needs to be formed on at least one of the outermost surfaces of the steel sheet 2, or it may be formed on both outermost surfaces of the steel sheet 2.

[0058] The Ni-plated surface-treated steel sheet 1 in this embodiment can be manufactured as follows.

[0059] First, a Ni plating layer is formed on the base steel sheet 2. As mentioned above, carbon steel containing Cu and Cr in predetermined proportions can be suitably used as the base steel sheet 2. The Cu content of the carbon steel used here is more preferably 0.05 to 1.0% by weight, and even more preferably 0.05 to 0.5% by weight. The Cr content of the carbon steel is more preferably 0.03 to 1.0% by weight, even more preferably 0.03 to 0.5% by weight, and particularly preferably 0.03 to 0.4% by weight. As the Ni plating bath used to form the Ni plating layer, commonly used plating baths, such as a watt bath, sulfamic acid bath, borofluoride bath, or chloride bath, can be used. For example, for the Ni plating layer, a Watt bath with a composition of 200g / L to 350g / L nickel sulfate hexahydrate, 20g / L to 60g / L nickel chloride hexahydrate, and 10g / L to 50g / L boric acid is used, with a pH of 3.0 to 5.0, a bath temperature of 40°C to 70°C, and a current density of 5A / dm². 2 ~40A / dm 2It can be formed under these conditions. The Ni plating layer only needs to be formed on at least one side of the steel sheet 2, but it is preferable to form it on both sides.

[0060] In this embodiment, from the viewpoint of forming the Fe-Ni-Cu-Cr layer 3 by facilitating the diffusion of Cu and Cr contained in the raw steel sheet 2 during the heat diffusion treatment process described later, it is preferable to add a small amount of a semi-gloss agent made of a sulfur-free compound such as an aliphatic unsaturated alcohol such as a polyoxyethylene adduct of an unsaturated alcohol, an unsaturated carboxylic acid, formaldehyde, and coumarin to the Ni plating bath. Specifically, the amount of semi-gloss agent added is preferably such that the total amount of semi-gloss agent in the plating bath is 0.6 mL / L to 6.0 mL / L, more preferably 0.8 mL / L to 5.0 mL / L, and even more preferably 1.2 mL / L to 5.5 mL / L. One type of semi-gloss agent may be used, or multiple types may be used in combination. When multiple types are combined, it is preferable that the total amount of the multiple types of semi-gloss agents falls within the above range.

[0061] The amount of Ni W deposited on the base sheet of steel sheet 2 by the formation of the Ni plating layer is not particularly limited as long as an Fe-Ni-Cu-Cr layer 3 can be formed as the outermost surface of the Ni-plated surface-treated steel sheet 1 and its composition can be controlled. However, if the amount of Ni deposited is too large, it becomes difficult for Fe, Cu, and Cr to diffuse to the outermost surface, and it becomes necessary to raise the heat treatment temperature or lengthen the heat treatment time in order to sufficiently diffuse Fe, Cu, and Cr, which may make it difficult to properly form the Fe-Ni-Cu-Cr layer 3. Therefore, 10.7 g / m² is recommended. 2 The following is preferable: 8.9 g / m 2 The following is more preferable: 8.0 g / m 2 The following is even more preferable: 7.2 g / m 2 The following is particularly preferable. On the other hand, if the amount of Ni deposited W is too small, it will be difficult to properly form the Fe-Ni-Cu-Cr layer 3, and the electrolyte resistance during over-discharge may decrease. Therefore, the amount of Ni deposited W is 0.45 g / m². 2 The above is preferable, 0.8 g / m 2 The above is more preferable, 2.5 g / m2 The above is even more preferable, 3.0 g / m 2 The above is particularly preferable. When the Fe-Ni-Cu-Cr layer 3 is formed on the outermost surface of both sides of the steel sheet 2, it is preferable to keep the amount of Ni deposited on each surface within the above range. Furthermore, when the Ni-plated surface-treated steel sheet 1 of this embodiment is used for a battery container in the shape of a can, it is preferable to form the Fe-Ni-Cu-Cr layer 3 on the outermost surface of the surface that will become the inner surface of the battery container, while forming an Fe-Ni diffusion layer on the surface that will become the outer surface of the battery container, and forming a Ni layer on top of the Fe-Ni diffusion layer. In order to achieve this configuration on the outer surface of the battery container, the amount of Ni deposited on the surface that will become the outer surface of the battery container is 9.0 g / m². 2 ~90g / m 2 It is preferable.

[0062] Next, a steel sheet (hereinafter referred to as the plated steel sheet) with a Ni plating layer formed on its surface is subjected to a thermal diffusion treatment to form an Fe-Ni-Cu-Cr layer 3. By appropriately controlling the conditions of the thermal diffusion treatment, an Fe-Ni-Cu-Cr layer 3 can be formed on the steel sheet.

[0063] The thermal diffusion treatment may be carried out by either a continuous annealing method or a box annealing method, and is not particularly limited, but it is preferable to use a non-oxidizing atmosphere or a reducing protective gas atmosphere for the heat treatment. When using a reducing protective gas atmosphere, it is preferable to use a mixed gas of H2 and N2 called HNX gas, for example. In this embodiment, the thermal diffusion treatment includes an initial heating step, a final heating step, and a cooling step.

[0064] The initial heating process is a process of heating the plated steel sheet from room temperature to the starting temperature of the final heating process (final heating start temperature), which will be described later. The heating rate in the initial heating process (hereinafter also referred to as the initial heating rate) is the rate obtained by calculating the slope of the temperature profile of the plated steel sheet in the initial heating process. In other words, it can be calculated by dividing the temperature difference from the starting temperature of the initial heating process to the starting temperature of the final heating process by the required time. It is preferable that the initial heating rate be greater than the heating rate in the final heating process, which will be described later. Specifically, the initial heating rate is preferably greater than 4°C / second and 14°C / second or less.

[0065] The maximum heating rate in the initial heating process (hereinafter also referred to as the maximum heating rate) is the rate obtained by calculating the maximum slope in the temperature profile of the plated steel sheet in the initial heating process, that is, the temperature profile from room temperature to the starting temperature of the final heating process, and is preferably 4°C / second or higher. Furthermore, from the viewpoint of appropriately forming the Fe-Ni-Cu-Cr layer 3 and controlling the Cu strength ratio and Cr strength ratio between the steel sheet 2 and the Fe-Ni-Cu-Cr layer 3 within an appropriate range, the maximum heating rate in the initial heating process is preferably 14°C / second or lower, more preferably 12°C / second or lower, and even more preferably 10°C / second or lower. In particular, from the viewpoint of suppressing the diffusion of Fe to the outermost surface, the maximum heating rate in the temperature profile of 450°C or higher in the initial heating process is preferably 14°C / second or lower, more preferably 12°C / second or lower, and even more preferably 10°C / second or lower.

[0066] The final heating step is a step of heating from the final heating start temperature to the maximum temperature in the heat diffusion treatment (hereinafter referred to as the "reached temperature"). The final heating start temperature is preferably 600°C or higher, where the Ni in the Ni plating layer and the Fe in the steel sheet 2 begin to diffuse actively, more preferably 650°C or higher, where mutual diffusion begins more actively, and even more preferably 680°C or higher, and particularly preferably 710°C or higher, from the viewpoint of promoting active diffusion of Cu and Cr in the final heating step. Furthermore, the final heating start temperature is preferably less than 900°C, more preferably less than 850°C. The reach temperature is preferably less than 930°C, more preferably less than 900°C, and even more preferably less than 870°C, from the viewpoint of properly forming the Fe-Ni-Cu-Cr layer 3. Note that the reach temperature can be set based on the final heating start temperature so that the temperature difference from the final heating start temperature is a predetermined temperature difference, as will be described later.

[0067] In this embodiment, from the viewpoint of improving the electrolyte resistance of the Ni-plated surface-treated steel sheet 1 during over-discharge as described later, the heating rate in the final heating step (hereinafter also referred to as the final heating rate) is preferably 4°C / second or less, more preferably 3°C / second or less, and even more preferably 1°C / second or less. The heating rate in the final heating step is preferably 0.1°C / second or more, and more preferably 0.2°C / second or more.

[0068] The temperature difference between the target temperature and the final heating start temperature should be 10°C or more, but preferably 30°C or more, and more preferably 40°C or more. If the temperature difference is too small, the heating time in the final heating process (final heating time) may be insufficient, and the desired alloy state of the Fe-Ni-Cu-Cr layer 3 may not be obtained. In particular, if the amount of Ni deposited is 2.5 g / m² 2If the temperature is above this, it is preferably 30°C or higher, more preferably 40°C or higher, and even more preferably 60°C or higher. By setting the temperature difference to 60°C or higher, the desired alloy state of the surface can be obtained, and a Ni-plated surface-treated steel sheet 1 with higher electrolyte resistance during over-discharge can be stably obtained. The upper limit of the temperature difference is preferably 150°C or lower, more preferably 120°C or lower, and even more preferably 100°C or lower. In this embodiment, it is preferable to set the final heating rate to 4°C / second or lower, so if the temperature difference is too large, the time spent in the high-temperature range will be too long, and the desired alloy state of the surface may not be obtained.

[0069] In the cooling process, the plated steel sheet, which has been heated to the target temperature, is cooled to 120°C or below. There are no particular restrictions on the cooling rate, but from the viewpoint of suppressing shape defects and wrinkles, 1°C / second to 20°C / second is preferred, and more preferably 1°C / second to 10°C / second.

[0070] Figure 2 shows an example of a temperature profile of a plated steel sheet to illustrate the method for calculating the thermal history Y in a thermal diffusion treatment.

[0071] From the viewpoint of improving the electrolyte resistance of the Ni-plated surface-treated steel sheet 1 during over-discharge, it is preferable, more preferable, that the thermal history Y applied to the plated steel sheet throughout the initial heating step, final heating step, and cooling step in the thermal diffusion treatment be 150,000°C·seconds or less, more preferable, that it be 120,000°C·seconds or less, and even more preferable, that it be 100,000°C·seconds or less. Furthermore, from the viewpoint of sufficiently thermally diffusing Fe and Ni to obtain the desired alloy state, it is preferable that the thermal history Y be 15,000°C·seconds or more, more preferable, that it be 35,000°C·seconds or more, and even more preferable, that it be 45,000°C·seconds or more. The thermal history Y can be determined by integrating the change in heating temperature and cooling temperature with respect to time at 450°C or higher. That is, the area of ​​the shaded portion in Figure 2 corresponds to the thermal history Y in the thermal diffusion treatment. To keep the thermal history Y applied to the plated steel sheet within the above range, the heating rate (including the maximum heating rate) above 450°C in the initial heating process and the final heating process, the starting temperature for heating, the target temperature, and the cooling rate in the cooling process should be appropriately adjusted.

[0072] If the thermal history Y in the thermal diffusion treatment is too large or too small, the desired alloy state cannot be obtained, and the electrolyte resistance during over-discharge tends to decrease.

[0073] Ni adhesion amount W (g / m 2 ) and the ratio of thermal history Y W / Y × 10 5 It is preferably 1.0 or greater. W / Y × 10 5 If the value is less than 1.0, the desired surface alloy state may not be obtained, and the electrolyte resistance during over-discharge may deteriorate. Also, the amount of Ni deposited W (g / m 2 ) and the ratio of thermal history Y W / Y × 10 5 It is preferably 20.0 or less, more preferably 10.0 or less, and even more preferably 7.0 or less. W / Y × 10 5 If the value exceeds 20.0, the diffusion of the metal may be insufficient, and the desired alloy state may not be achieved.

[0074] As described above, the inventors have found that by controlling the amount of Ni deposited on the steel sheet W within the above range and performing the thermal diffusion treatment of the Ni-plated steel sheet under the above conditions, the Ni in the Ni-plating layer and the Fe, Cu, and Cr in the steel sheet 2 mutually diffuse, and an Fe-Ni-Cu-Cr layer 3 can be formed on the steel sheet 2. The Ni-plated surface-treated steel sheet 1 manufactured by the above method has excellent electrolyte resistance during over-discharge due to the presence of the Fe-Ni-Cu-Cr layer 3.

[0075] Conventionally, a method has been known to improve the electrolyte resistance of Ni-plated steel sheets by performing a thermal diffusion treatment on a steel sheet with a Ni-plated layer to form an Fe-Ni diffusion layer. In contrast, the present inventors have found that by diffusing not only Fe but also Cu and Cr contained in the steel sheet 2, and forming an Fe-Ni-Cu-Cr layer 3 on the steel sheet 2, the Ni-plated surface-treated steel sheet 1 can be made to have even better electrolyte resistance.

[0076] The reason why the above thermal diffusion treatment method can form the Fe-Ni-Cu-Cr layer 3 is not entirely clear, but the following is considered possible. First, the diffusion coefficients of nickel and chromium in iron are similar, and the diffusion coefficient of copper is slightly higher but still roughly the same. Chromium diffuses actively above 700°C, and its diffusion rate drops significantly below 700°C. Copper also begins to diffuse actively above 700°C. Therefore, in the above thermal diffusion treatment method, by gradually increasing the temperature during the initial heating, the diffusion of copper and chromium can be suppressed, preventing a copper and chromium deficiency near the interface. Furthermore, in the above thermal diffusion treatment method, heating to above 700°C in the final heating step can promote the movement of copper and chromium from the interface to the surface. It is thought that this diffusion mechanism of copper and chromium makes it possible to form the Fe-Ni-Cu-Cr layer 3, which contains not only iron but also copper and chromium. Furthermore, by continuing to raise the temperature during the final heating process, it is possible to suppress the rapid change from the nickel crystal structure to the iron-nickel alloy crystal structure, thereby preventing the diffusion routes of copper and chromium from being obstructed, and thus obtaining an Fe-Ni-Cu-Cr layer 3 that contains sufficient, albeit trace amounts, of copper and chromium on its surface.

[0077] Furthermore, a more preferable Fe-Ni-Cu-Cr layer 3 can be obtained by forming the Ni plating layer before thermal diffusion using a Ni plating bath containing a small amount of semi-brightener. A Ni plating layer formed using a nickel plating bath containing a small amount of semi-brightener contains more plating strain than a Ni plating layer formed using a matte Ni plating bath. Therefore, when the plating strain is released during the thermal diffusion treatment, the driving force of atoms due to the change in crystal structure can be increased. As a result, in the diffusion from the steel sheet to the Ni plating layer, especially in the diffusion during the final heating process, not only iron but also copper and chromium can diffuse more easily, and a more preferable Fe-Ni-Cu-Cr layer 3 can be obtained. On the other hand, if too much semi-brightener is added to the Ni plating bath, the crystal grains of the Ni plating layer will become smaller, and the addition of copper and chromium may make the Fe-Ni-Cu-Cr layer 3 too hard. Therefore, it is preferable to add 6.0 mL / L or less of semi-brightener.

[0078] As described above, the Ni-plated surface-treated steel sheet 1 in this embodiment is manufactured.

[0079] Furthermore, after the heat diffusion treatment, temper rolling may be performed on the Ni-plated surface-treated steel sheet as needed. Temper rolling allows for control of mechanical properties, shape correction, and the application of surface roughness.

[0080] <Battery container> The battery container in this embodiment is obtained by forming the Ni-plated surface-treated steel sheet 1 such that the surface on which the Fe-Ni-Cu-Cr layer 3 is formed faces the inside of the battery container. Specifically, the Ni-plated surface-treated steel sheet 1 can be formed into the shape of a battery container by press forming such as drawing, ironing, DI (Drawing and Ironing), or DTR (Draw and Thin Redraw). The shape of the battery container can be cylindrical, rectangular, pouch-type, or cup-type, as well as those with protrusions or holes on a part of the plate shape, such as a lid, current collector plate, or terminals.

[0081] The battery container obtained by forming the Ni-plated surface-treated steel sheet 1 in this embodiment has a high electrolytic solution resistance during over-discharge because the Fe-Ni-Cu-Cr layer 3 is formed on the inner surface side, and the occurrence of corrosion due to the elution of Fe can be suppressed.

Examples

[0082] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. The evaluation methods for each characteristic are as follows.

[0083] <Ni plating layer thickness> In the plated steel sheets on which the Ni plating layer was formed in each example and comparative example, the Ni adhesion amount per one surface of the Ni-plated steel sheet was determined by measuring with a fluorescent X-ray device. As the fluorescent X-ray device, ZSX100e (manufactured by Rigaku Corporation) was used, and the measurement was performed by the calibration curve method. The Ni plating layer thickness was obtained by converting the Ni adhesion amount into thickness using the density of Ni (8.9 g / cm 3 )

[0084] <Strength, strength ratio, and Fe-Ni-Cu-Cr layer thickness of each metal by GDS> Using a high-frequency glow discharge emission spectrometer (Horiba, Ltd., model number: GD-PROFILER2), the etching rate of Ni was first determined to be 0.035 μm / sec using a standard Ni-plated steel sheet (standard sample) with a thickness of 1.1 μm of matte Ni plating on a 0.3 mm thick low-carbon steel sheet, according to the method described above. The maximum value of Ni intensity in the standard Ni-plated steel sheet, as well as the Cu and Cr intensities at depths of 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, and 0.9 μm, were also confirmed. Next, measurements were taken on Ni-plated surface-treated steel sheet 1, and the changes in Fe intensity, Ni intensity, Cu intensity, and Cr intensity with respect to measurement time (etching time) were measured. Based on the etching rate of Ni, the measurement time (etching time) for high-frequency glow discharge emission spectrometer analysis on Ni-plated surface-treated steel sheet 1 was converted to depth. The resulting charts are shown in Figures 3(a) to 5(b). Figure 3(a) is a chart obtained by high-frequency glow discharge emission spectroscopy of Example 1, and Figure 3(b) is an enlarged view of Figure 3(a). Figure 4(a) is a chart obtained by high-frequency glow discharge emission spectroscopy of Example 2, and Figure 4(b) is an enlarged view of Figure 4(a). Figure 5(a) is a chart obtained by high-frequency glow discharge emission spectroscopy of Comparative Example 1, and Figure 5(b) is an enlarged view of Figure 5(a).

[0085] In the obtained chart, the formation of Fe-Ni-Cu-Cr layer 3 was confirmed by comparing it with a standard Ni-plated steel sheet using the method described above. Furthermore, the Cu and Cr intensities were determined at depths of 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, and 0.9 μm. Additionally, the depth D at which the Ni intensity reached 2% of the maximum Ni intensity of the standard sample was determined. Ni2% The Cu strength and Cr strength in steel plate 2 are shown, and the Cu strength in steel plate 2 is shown. Cu-steel and Cr strength In Cr-steel The maximum value of Cu strength in each Ni-plated surface-treated steel sheet 1 was determined as follows: Cu-MAX and the maximum value of Cr intensity In Cr-MAXThe depth at which the maximum value is obtained was also determined. In addition, the Cu strength at the depth where the Ni strength is 10%, which is the boundary point between the Fe-Ni-Cu-Cr layer 3 and the steel plate 2, was measured, and the thickness of the Fe-Ni-Cu-Cr layer 3 was determined from that depth. Furthermore, the maximum value of the Fe strength of the standard sample In Fe―MAX-ref Fe strength at a depth of 0.1 μm from the surface side relative to 10% of the value In Fe-0.1d Ratio IR Fe-0.1d They sought it.

[0086] Cu intensity at a depth of 0.1 μm from the surface side In Cu-0.1d and the Cu strength in steel plate 2 Cu-steel Ratio IR Cu-0.1d Similarly, the Cu intensity ratio IR at depths of 0.3 μm, 0.5 μm, 0.7 μm, and 0.9 μm was determined. Cu-0.3d IR Cu-0.5d IR Cu-0.7d , and IR Cu-0.9d The following values ​​were determined for each. Similarly, the Cr intensity ratio IR at depths of 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, and 0.9 μm was also determined. Cr-0.3d IR Cr-0.5d IR Cr-0.7d , and IR Cr-0.9d The maximum value of Cu intensity In was also determined. Cu-MAX and the maximum value of Cr intensity In Cr-MAX Furthermore, the Cu strength in steel plate 2 is In Cu-steel These ratios to IR Cu-MAX and IR Cr-MAX The following were determined for each sample. Furthermore, the Cu intensity at a depth of 0.5 μm of the standard sample was determined. Cu-0.5d-ref Cu intensity ratio at each depth position relative to IR Cu-d-vref , and the Cr intensity at a depth of 0.5 μm in the standard sample. Cr-0.5d-ref Cr intensity ratio at each depth position relative to IR Cr-d-vref They sought it. The specific measurement conditions for the high-frequency glow discharge emission spectrometer were as follows: • Measurement mode: HDD mode • Excitation mode: RF (Normal) Output: 35W • Pressure: 600 Pa Module: 7V Fuse: 5V • Anode diameter: 4mm • Gas replacement time: 30 seconds • Pre-sputtering time: 30 seconds • Background measurement time: 5 seconds Measurement time: 100 seconds • Sampling interval: 0.1 seconds

[0087] <Evaluation of electrolyte resistance during over-discharge> The electrolyte resistance under over-discharge conditions was evaluated for Ni-plated surface-treated steel sheet 1 using the Linear Sweep Voltammetry (LSV) method with a multi-electrochemical measurement system HZ-Pro (model: HAG-PROM12, manufactured by Hokuto Denko Co., Ltd.). The measurement jig shown in Figure 6 was used for the measurement. Figure 6 is a schematic diagram of the measurement jig used for evaluating the electrolyte resistance of Ni-plated surface-treated steel sheet 1 using the LSV method. As shown in Figure 6, the Ni-plated surface-treated steel sheet 1 was attached to the bottom of the measurement jig, an electrolyte (1 mol / L LiPF6, EC:DEC (1:1 v / v%), manufactured by Kishida Chemical Co., Ltd.) was added to the jig, and metallic lithium (manufactured by Honjo Metal Co., Ltd.) was attached to the upper electrode of the jig as the counter electrode and reference electrode. The surface area of ​​the measurement surface was 1.04 cm². 2 The surface area of ​​the counter electrode and the reference electrode is 1.2 cm². 2 The following settings were used: the distance between the reference electrode and the working electrode was set to 2 mm, the distance between the counter electrode and the working electrode was set to 2 mm, and the distance between the counter electrode and the reference electrode was set to 12 mm. The measurements were performed in a dry room with a dew point of -40°C or lower and a room temperature of 23°C. From the natural potential, a scanning speed of 2 mV / sec was used to obtain the equivalent of over-discharge, +4.1 V (vsLi / Li). + ) is polarized to, and the current value at 4.1V is (μA / cm 2 The electrolyte resistance of Ni-plated surface-treated steel sheet 1 during over-discharge was evaluated by measuring the current value. A smaller current value indicates less metal leaching, such as Fe, and superior electrolyte resistance during over-discharge.

[0088] <Contact resistance value> The Ni-plated surface-treated steel sheet 1 was cut to produce a test piece with a size of 25 mm square. Next, one of the produced test pieces was measured using an electric contact simulator (manufactured by Yamazaki Precision Research Institute, model number: CRS-1) under the condition of a contact load of 150 gf to measure the contact resistance value [mΩ]. A smaller contact resistance value indicates that the Ni-plated surface-treated steel sheet 1 has excellent battery characteristics when used as a battery container.

[0089] <<Example 1>> As the base plate of the steel sheet 2, a cold-rolled steel sheet (low-carbon steel A) with a thickness of 0.5 mm of low-carbon aluminum-killed steel in which the Cu content is 0.2 wt% or more and 0.4 wt% or less and the Cr content is 0.1 wt% or more and less than 0.3 wt% was prepared.

[0090] Then, for the prepared cold-rolled steel sheet, after performing alkaline electrolytic degreasing and pickling in sulfuric acid immersion, electroplating (Ni plating) was performed using a Ni plating bath with the following bath composition under the following conditions, and a Ni plating layer with a Ni deposition amount W of 4.45 g / m 2 was formed on the surface of the cold-rolled steel sheet to obtain a plated steel sheet. <Ni Plating Conditions> Bath composition: Nickel sulfate hexahydrate 250 g / L, Nickel chloride hexahydrate 45 g / L, Boric acid 30 g / L, Semi-brightener (unsaturated alcohol polyoxyethylene adduct, unsaturated carboxylic acid, formaldehyde) 3.0 mL / L pH: 4.0 - 5.0 Bath temperature: 60 °C Current density: 10 A / dm 2

[0091] Next, the steel sheet with the Ni plating layer (plated steel sheet) was subjected to thermal diffusion treatment by continuous annealing under a reducing protective gas atmosphere to form an Fe-Ni-Cu-Cr layer 3. After the thermal diffusion treatment, temper rolling with a reduction ratio of 3% or less was performed to obtain a Ni-plated surface-treated steel sheet 1 comprising a steel sheet 2 and an Fe-Ni-Cu-Cr layer 3 provided on one side of the steel sheet 2. In the continuous annealing, in the initial heating step, the plated steel sheet was heated from room temperature to the final heating start temperature. The final heating start temperature was set within the temperature range of 660 to 694°C. The maximum heating rate in the initial heating step was 4.96°C / second. Next, in the final heating step, the target temperature was set within the temperature range of 695 to 729°C so that the difference between the final heating start temperature and the final heating target temperature (temperature difference in the final heating step) was 40°C, and the plated steel sheet was heated at a heating rate of 0.37°C / second. Next, as a cooling process, the plated steel sheet was cooled to below 120°C by blowing a cooling gas such as HNX gas onto it. The total thermal history Y applied to the Ni-plated steel sheet throughout the initial heating process, final heating process, and cooling process was 57920°C·seconds.

[0092] The obtained Ni-plated surface-treated steel sheet 1 was evaluated according to the method described above. The results are shown in Table 1. In Table 1, the Cu strength and Cr strength at each depth position are collectively referred to as In, respectively. Cu-d , and In Cr―d This was written as follows. In addition, the ratio of the Cu strength at each depth position to the Cu strength in steel plate 2 was collectively referred to as IR. Cu-d This is expressed as IR, and the ratio of the Cr strength at each depth position to the Cr strength in steel plate 2 is collectively referred to as IR. Cr-d This was written as follows.

[0093] <<Example 2>> Except for changing the base material of steel sheet 2 to a 0.5 mm thick cold-rolled steel sheet of low-carbon aluminum-killed steel (low-carbon steel B) with a Cu and Cr content of 0.01% or more and less than 0.05% by weight, a Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

[0094] <<Example 3>> Except for changing the base sheet of steel sheet 2 to a 0.5 mm thick cold-rolled steel sheet (low-carbon steel C) of low-carbon aluminum-killed steel with a Cu content of 0.1% or more and less than 0.2% by weight and a Cr content of 0.03% or more and less than 0.05% by weight, and performing the heat diffusion treatment under the conditions described in Table 5, a Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 1 and evaluated in the same manner.

[0095] <<Examples 4-5>> Except for performing the heat diffusion treatment under the conditions described in Table 5, a Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 3 and evaluated in the same manner.

[0096] <<Example 6>> The amount of Ni plating deposited was 0.89 g / m². 2 Except for the change and the heat diffusion treatment being carried out under the conditions described in Table 5, Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 3 and evaluated in the same manner.

[0097] <<Examples 7 and 8>> The amount of Ni plating deposited is 2.67 g / m². 2 Except for the change and the heat diffusion treatment being carried out under the conditions described in Table 5, Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 3 and evaluated in the same manner.

[0098] <<Example 9>> Except for changing the base material of steel sheet 2 to a 0.5 mm thick cold-rolled steel sheet (low-carbon steel D) of low-carbon aluminum-killed steel with a Cu content of 0.05% or more and less than 0.1% by weight and a Cr content of 0.03% or more and less than 0.05% by weight, and performing the heat diffusion treatment under the conditions described in Table 5, Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 1 and evaluated in the same manner.

[0099] <<Example 10>> The amount of Ni plating applied was 6.68 g / m². 2 Except for the change and the heat diffusion treatment being carried out under the conditions described in Table 5, Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 3 and evaluated in the same manner.

[0100] <<Example 11>> Except for changing the base material of steel sheet 2 to low-carbon steel D, a Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 10 and evaluated in the same manner.

[0101] <<Example 12>> Except for changing the base material of steel sheet 2 to low-carbon steel B, a Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 11 and evaluated in the same manner.

[0102] <<Comparative Example 1>> Ni adhesion amount: 8.9 g / m 2 Except for the change and the absence of thermal diffusion treatment, a Ni-plated steel sheet was obtained in the same manner as in Example 2 and evaluated in the same manner. The results are shown in Table 1. In Comparative Example 1, the intensity of each element in high-frequency glow discharge emission spectroscopy was about the same as that of the standard Ni-plated steel sheet, so it was determined that the Fe-Ni-Cu-Cr layer 3 was not formed. In addition, it was confirmed that the numerical values ​​of the Cu intensity ratio and Cr intensity ratio with steel sheet 2 at each depth position of the Ni-plated layer in Comparative Example 1 were less than 0.5 and less than 0.2, respectively.

[0103] <<Comparative Example 2>> Ni-plated steel sheets were obtained in the same manner as in Example 10, except that the thermal diffusion treatment was performed under the conditions described in Table 5, and were evaluated in the same manner.

[0104] <<Comparative Example 3>> The amount of Ni plating applied is 8.9 g / m 2 Except for the change made, a Ni-plated steel sheet was obtained in the same manner as in Example 10 and evaluated in the same manner.

[0105] [Table 1]

[0106] [Table 2]

[0107] [Table 3]

[0108] [Table 4]

[0109] [Table 5]

[0110] As shown in Tables 1 to 3, in Examples 1 to 12, when comparing the individual strengths of the standard nickel-plated steel sheet and the individual strengths of the Ni-plated surface-treated steel sheet 1, measured by high-frequency glow discharge emission spectroscopy, there were alloy regions where the Fe and Ni strengths were 10% or more of the maximum strength of the standard Ni-plated steel sheet, and the Cu and Cr strengths were higher than the individual strengths in the Ni plating layer of the standard Ni-plated steel sheet. From this, it was confirmed that an alloy region in which Fe, Ni, Cu, and Cr are all present, i.e., an Fe-Ni-Cu-Cr layer 3, was formed. Specifically, it was clear that the above-mentioned alloy regions existed at least at depth positions of 0.1 μm, 0.3 μm, and 0.5 μm, and it was confirmed that the strength ratio to the standard Ni-plated steel sheet at each position was 2.0 or higher for both Cu and Cr, i.e., a strength ratio of more than 2 times was obtained. Furthermore, in Examples 1 to 12, the strength ratio IR between the depth position of 0.1 μm and steel sheet 2 was also found. Cu-0.1d It was confirmed that the ratio was between 0.5 and 3.0. In addition, in Examples 1 to 12, the strength ratio IR between the depth position of 0.5 μm and the steel plate 2 was found to be between 0.5 μm and 3.0. Cu-0.5d The value is 0.5 or higher, IR Cr-0.5d It was confirmed that the value was 0.20 or higher.

[0111] As shown in Tables 1 to 3, the Ni-plated surface-treated steel sheet 1 with the Fe-Ni-Cu-Cr layer 3 exhibited a low current value due to metal elution such as Fe at 4.1V, equivalent to over-discharge, and showed excellent electrolyte resistance during over-discharge (Examples 1-12). In particular, Example 1 showed a current value approximately 60% lower than Comparative Example 1 shown in Table 4, demonstrating particularly excellent electrolyte resistance. Furthermore, the Ni-plated surface-treated steel sheet 1 of Example 1 showed a higher Cr intensity at a depth of 0.5 μm in the standard sample than the Ni-plated surface-treated steel sheet 2 of Example 2. Cr-0.5d-ref Cr intensity ratio at each depth position relative to IR Cr-d-vref Although the coefficient of carbon was high, the contact resistance was about the same. This is thought to be because, in Example 1, although there is a lot of Cr, a sufficient amount of Cu also diffuses from the steel plate 2 and is included in the Fe-Ni-Cu-Cr layer 3.

[0112] Furthermore, in Example 1, the strength ratio IR between the depth position of 0.5 μm and the steel plate 2 was Cu-0.5d It was confirmed that the ratio was 0.5 or higher. In addition, in Example 1, the difference IR of the Cu intensity ratio was Cu-MAX -IR Cu-0.1d The value is greater than 0.05, satisfying equation (1) above, and the difference IR of the Cu intensity ratio. Cu-MAX -IR Cu-boundary The ratio was greater than 0.05, satisfying equation (2) above. In other words, in Example 1, it was confirmed that there is a region where copper is concentrated in the intermediate region of the Fe-Ni-Cu-Cr layer 3. This can be confirmed from the fact that the depth at which the maximum Cu intensity in Example 1 is 0.59 μm, which is shallower than the boundary point with the steel plate 2, and from the fact that, unlike Example 2 and Comparative Example 1, in the chart diagram of Example 1, as shown in Figure 3(b), the Cu intensity decreases towards the boundary point with the steel plate 2 after reaching the maximum Cu intensity. Furthermore, in Example 1, the Cu intensity ratio IR with the standard sample was observed over the entire range from a depth of 0.1 μm to 0.5 μm from the surface. Cu-d-vrefThe value was between 2.3 and 10, which was higher than in Example 2. From this, it can be said that Example 1 had a larger absolute amount of Cu near the surface compared to Example 2. Compared to Example 2, Example 1 had a smaller current value caused by the dissolution of metals such as Fe at 4.1V, which corresponds to over-discharge, and demonstrated particularly excellent electrolyte resistance during over-discharge. It is thought that this result was obtained in Example 1 by using carbon steel with a particularly high Cu content compared to Example 2.

[0113] As shown in Examples 3-5, even when using carbon steel C with a Cu content of 0.1% by weight or more and less than 0.2% by weight, and a Cr content of 0.03% by weight or more and less than 0.05% by weight, a Ni-plated surface-treated steel sheet 1 with excellent electrolyte resistance was obtained.

[0114] As shown in Table 2, even when the amount of Ni plating is relatively small, the Fe-Ni-Cu-Cr layer 3 is formed using carbon steel containing predetermined amounts of Cu and Cr as the base plate, and the strength ratio IR between the depth position 0.1 μm and the steel plate 2 is... Cu-0.1d By setting the value to 0.5 or more and 3.0 or less, the Ni-plated surface-treated steel sheet 1 exhibited excellent resistance to electrolytes (Examples 6-9).

[0115] As shown in Table 3, when the amount of Ni plating is relatively large, the Cu strength ratio IR with respect to the steel plate is Cu-d or Cu intensity ratio IR with standard sample Cu-d-vref However, the values ​​were relatively small, especially near the surface (Examples 10-12). Nevertheless, as can be seen from the comparison with Comparative Example 2 shown in Table 4, even when the amount of Ni plating was relatively large, the Fe-Ni-Cu-Cr layer 3 was formed, and the strength ratio IR between the depth position 0.1 μm and the steel plate 2 was also observed. Cu-0.1d By setting the value between 0.5 and 3.0, we were able to improve the electrolyte resistance.

[0116] On the other hand, the Ni-plated steel sheet in which the formation of the Fe-Ni-Cu-Cr layer was not observed showed a large current value due to the dissolution of Fe at 4.1V, which corresponds to over-discharge, and had poor electrolyte resistance (Comparative Example 1).

[0117] Furthermore, even when the Fe-Ni-Cu-Cr layer 3 is formed, the strength ratio IR between the depth position 0.1 μm and the steel plate 2 is also Cu-0.1d When the value was less than 0.5, indicating insufficient diffusion of Cu near the surface, the electrolyte resistance was poor (Comparative Example 2-3). [Explanation of Symbols]

[0118] 1…Ni-plated surface-treated steel sheet 2...Steel plate 3…Fe-Ni-Cu-Cr layer

Claims

1. A Ni-plated surface-treated steel sheet comprising a steel sheet made of carbon steel and an Fe-Ni-Cu-Cr layer formed on at least one surface of the steel sheet, When the Cu intensity of the Fe-Ni-Cu-Cr layer was continuously measured from the surface side toward the depth direction by high-frequency glow discharge emission spectroscopy (GDS), the Cu intensity in the steel sheet was determined to be In Ｃｕ－ｓｔｅｅｌ Cu intensity at a depth of 0.1 μm from the surface side relative to In Ｃｕ－０．１ｄ Ratio IR Ｃｕ－０．１ｄ However, the Ni-plated surface-treated steel sheet has a value of 0.5 or more and less than 3.

0.

2. When the Cu intensity of the Fe-Ni-Cu-Cr layer was continuously measured from the surface side toward the depth direction by high-frequency glow discharge emission spectroscopy (GDS), the Cu intensity in the steel sheet was determined to be In Ｃｕ－ｓｔｅｅｌ Cu intensity at a depth of 0.5 μm from the surface side relative to In Ｃｕ－０．５ｄ Ratio IR Ｃｕ－０．５ｄ However, the Ni-plated surface-treated steel sheet according to claim 1, wherein the ratio is 0.5 or more and less than 3.

0.

3. When continuously measuring the Cr intensity in the depth direction from the surface side of the Fe—Ni—Cu—Cr layer by high-frequency glow discharge optical emission spectroscopy (GDS), the Cr intensity In Ｃｒ－ｓｔｅｅｌ at the position of a depth of 0.5 μm from the surface side with respect to the Cr intensity In Ｃｒ－０．５ｄ in the steel sheet has a ratio IR Ｃｒ－０．５ｄ of 0.2 or more and less than 2.0, the Ni-plated surface-treated steel sheet according to claim 1 or 2.

4. When the Cr intensity of the Fe-Ni-Cu-Cr layer was continuously measured from the surface side toward the depth direction by high-frequency glow discharge emission spectroscopy (GDS), the Cr intensity in the steel sheet was determined to be In Ｃｒ－ｓｔｅｅｌ Cr intensity at a depth of 0.1 μm from the surface side relative to In Ｃｒ－０．１ｄ Ratio IR Ｃｒ－０．１ｄ However, the Ni-plated surface-treated steel sheet according to claim 1 or 2, wherein the ratio is 0.2 or more and less than 2.

0.

5. When the Cu intensity of the Fe-Ni-Cu-Cr layer was continuously measured from the surface side toward the depth direction by high-frequency glow discharge emission spectroscopy (GDS), the Cu intensity in the steel sheet was determined to be In Ｃｕ－ｓｔｅｅｌ Cu strength at a depth of 0.3 to 0.7 μm from the surface side relative to In Ｃｕ－０．３ｄ～０．７ｄ Ratio IR Ｃｕ－０．３ｄ～０．７ｄ However, the Ni-plated surface-treated steel sheet according to claim 1 or 2, wherein the ratio is 0.5 or more and 3.0 or less.

6. The Ni-plated surface-treated steel sheet according to claim 1 or 2, wherein the Fe-Ni-Cu-Cr layer has a Cu-enriched region.

7. When the Cu intensity of the Fe-Ni-Cu-Cr layer was continuously measured from the surface side toward the depth direction by high-frequency glow discharge emission spectroscopy (GDS), the Cu intensity in the steel sheet was determined to be In Ｃｕ－ｓｔｅｅｌ The maximum Cu strength in the depth up to the steel plate is In ＭＡＸ Ratio IR Ｃｕ－ＭＡＸ However, the Ni-plated surface-treated steel sheet according to claim 1 or 2, wherein the ratio is greater than 0.8 and less than or equal to 3.

0.

8. The Ni-plated surface-treated steel sheet according to claim 1 or 2, wherein the steel sheet is low-carbon steel or ultra-low-carbon steel.

9. The steel plate is low-carbon steel, The Cu content in the steel sheet is 0.01% by weight to 1.0% by weight. The Ni-plated surface-treated steel sheet according to claim 1 or 2, wherein the Cr content in the steel sheet is 0.01% by weight to 1.0% by weight.

10. A battery container made using a Ni-plated surface-treated steel sheet according to claim 1 or 2.

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